Uber analysis for this month:
1. Kyogre (=)
2. Darkrai (+2)
3. Rayquaza (-1)
4. Dialga (+1)
5. Groudon (-2)
6. Palkia (+1)
7. Lugia (+1)
8. Mewtwo (-2)
9. Scizor (=)
10. Blissey (+3)
11. Deoxys-f (=)
12. Latias (+2)
13. Giratina (-1)
14. Garchomp (+3)
15. Giratina-o (+5)
16. Deoxys-e (-6)
17. Tyranitar (+2)
18. Mew (-3)
19. Metagross (-3)
--- OU cut-off point
20. Ho-oh (+2)
21. Forretress (=)
22. Wobbuffet (+6)
23. Celebi (+9)
24. Latios (+1)
25. Deoxys-l (+1)
Top leads: Darkrai, who led a whopping 2.4 times more than the #2 lead, Deoxys-f.
My prediction last month did not come true. Neither Rayquaza nor Groudon have taken the #1 spot, and Kyogre remains the #1 most used pokemon (and as of right now, I don't see that changing) and by a respectable margin. For the first time in this ladder's history, the RSE trio's grip on the top 3 has been shattered. There are a number of reasons for this. One battler, by himself, had significantly impacted usage by himself by using the same team repeatedly (Darkrai/Dialga/Groudon/Mewtwo/Scizor/Rayquaza). Out of the 4249 uber battles last month, he played in a staggering 1022 of them, meaning that he is responsible for approximately 12% of all usages that month. To my knowledge, he has played very little this month, so any conclusions on shifts in usages must keep this in mind. Second, Darkrai and Dialga still rose this month (especially for the former). I'll go into more detail on these individually.
As I mentioned above, Kyogre remains at #1, virtually unphased by the metagame shifts. Surprisingly, the Choice Scarf set was more common this month, for some reason. This doesn't really make sense considering that most things that the scarfer dislikes dealing with has risen in usage. More DD Rays, similar ScarfPalkias, more Blisseys, more Latias, more bulky Dialgas. Specs or CM both look clearly superior. I've had very little trouble with them with any of my teams, and I really don't know what to make of it. Timid Scarfers can take out Adamant DD Ray, but that's about all I see. Specs is still strong though, followed distantly by a straight CM set (usually with lefties; and which I've been told has worked well, but, for me anyway, has only forced me to reveal more of my team midgame) and restalk sets. Few CMRestalkers though (supported by even lower Defense-heavy spreads on the restalkers); those that I have encountered have actually chosen Ice Beam over Surf.
Darkrai usage continued to skyrocket this month, launching him to #2 for the first time, but his climb should stop here. As widespread as the Choice Scarf, Trick, and Nasty Plot sets have become, people are experimenting with checks. Scizor usage was relatively higher this month, and I've also seen a surprisingly effective anti-lead Celebi, a Sleep Talk Kyogre with three attacks, and more Wobbuffets.
Rayquaza has dropped to #3, but he's still quite popular. The SD set has dropped further in popularity in favor of DD. This is likely because the SD set is walled by mostly the same things as the DD set at the moment and that DD already has enough power to hurt what it needs to hurt right now, "so why bother". The general trend, however, is still towards Boosting Move/Dragon Move/Extreme Speed/Miscellaneous Coverage Move (in that order of likelihood). Although I haven't used it recently, I'd wager ES is still useful on the DD sets for picking off miscellaneous threats and for kamikaze strikes and is still more useful than two miscellaneous coverage moves. EQ has dropped in usage somewhat, but that's probably because Outrage already hurts Dialga enough and Scizor is the other most common Steel now. Allot of people are plugging that last slot with a fire move, evidently, although I can't vouch for this from personal experience as opposing Rays have rarely used anything other than Boosting Move/Dragon Move on me. Mixed Rays and CBers (surprisingly) fill out the remaining usage, which aim to catch Ray's usual counters off-guard with no set-up sets, although they're both relatively small in number. Mixed sets did rise this month, but not as much as predicted. Odds look favorable for them this month, but only if DD declines, which is a possibility but still early to tell. SD sets will not regain their former popularity, not any time soon.
Dialga is back to #4, serving primarily as a special attacker and/or special tank. Its two most common moves, by far, were Draco Meteor and Thunder. Thunder is a staple in many sets, but the disparity in usage between Thunder's usage and other moves that would typically be present along with it means people are using Dialga as a Kyogre counter more than before (which again begs the question "why are people running Scarfogre?"). Support/Bulky Attacker, BURestalk, Mixed, and Scarfed follow in what should be that order, which makes sense. Dialga may be the best restalker right now, and the Scarf set has less to prey on.
Groudon has dropped to #5, another first for this ladder. He hasn't gotten any worse - it's just that the services of all the pokemon above him are more called upon than his own. Rock Polish is still the most common set, but SD and support sets now follow closely behind.
Choice Scarf Palkia is still the most popular variant by far but has given way slightly to Lustrous Orb. Palkia's moves this month are slightly more varied too. More people are running Aura Sphere, Fire Blast, and Outrage (probably over Draco Meteor) and preferring Thunder over Surf.
Lugia usage remains steady. The spreads are slightly more varied this time (some emphasize Defense over Speed and vice versa), but there are otherwise no significant changes. While it may seem that Palkia and Lugia have made some gains this month, Mewtwo's drop in usage is the real reason they're higher up. Mewtwo himself functions virtually the same as he did last month, but some of the perceived changes this month (more scarfers, DD Ray) hurt him.
Scizor saw relatively more use this month, solidifying his position as the premier Steel trapper over Metagross, whose usage has in turn dropped significantly. The drop in Mew and Deoxys-e usage usage leaves fewer Scizor carrying Brick Break.
In response to the considerable rise of special threats this month, Blissey usage has shot up this month. The sets are largely the same, but more Blissey that weren't already running Defense EVs before are running them now.
Deoxys-f remains unchanged. Mewtwo generally serves its role better at the moment, but it's still a respectable lead.
Latias was also used more this month, surprisingly. The sets are very similar to last months', but the spreads are different. More maxed HP, ran some Defense, ran much less Special Attack, and ran a little less Speed. Fewer ran Grass Knot (and more HP Fire), so this may have been for Scizor instead. I'm also assuming they were counting on Stealth Rock damage for Palkia or have another pokemon for dealing with Palkia, since an unboosted Dragon Pulse with no SpA EVs will never OHKO it without residual damage.
Giratina is largely being passed over for Lugia for physical walling at the moment, as Lugia deals with most physical threats (bar Groudon) better. Given the state of the metagame, I'm surprised the Wow set is more popular than the CMer.
Garchomp was used primarily as a revenge killer. Sets were mostly Choice Scarf this month, and Garchomp had few problems switching in and out to pick off threats with Earthquake and Dragon Claw early on and then using Outrage later on. Many used Outrage immediately, and there's not much that could switch in, take it out, and make it out alive.
Giratina-o is finally "OU". Given that its typing is a big double-edged sword and that it's not raw power incarnate, I doubt it will rise much higher on the ladder, but this vicinity is where it belongs. Substitute sets dominated to make up for its lack of speed (and, to a lesser extent, to battle stall). Most ran either CM or mixed sets.
Deoxys-es and Mews have settled down in response to being directly anti-metagamed. They dropped regularly through the month.
Tyranitars increased this month, although it's not just because of Garchomp. Most of the Tyranitars I saw were on teams without Garchomp, actually. Nearly all of them were Choice Banders, meant to pick off specific prey or just take a chunk of damage out of something. There were a fewer Dragon Dancers and Subbers, but Tyranitar has a tough time setting up at the moment and the immediate power of CB is generally more threatening than its other sets. Most of the spreads favored HP and Special Defense over Attack this month.