I'm rather torn in my opinions. I don't find Skymin to be broken per se - there, if not counters, things which shut it down the vast majority of the time. However, there's always that 10% of the time when Skymin's ability to abuse luck simply becomes too great. I am kind of leaning towards a Skymin nomination not because I think it is over-powering, but because I don't think a metagame with Skymin is one I want to play, for it involves too much luck. I think this leads back to what was being discussed in Policy Review earlier - what kind of metagame do we want? I'd argue the metagame we want is one where the majority of players are happy with it, simple as that, and I don't think that we can create a metagame which pleases people with the level of luck Skymin introduces.
So yeah, I have three proposals as suspects: Darkrai (don't think there's any dissent on that issue, he's a monster), and Skymin and Inconsistent (to be banned as an ability), for making the metagame one which is not desirable.
Everything else is manageable. Doryuzuu is tricky to play around, but ultimately there are some checks and even one or two counters. Manaphy is absolutely brutal in rain, but I think weather control is a key skill in BW, and robbed of rain Manaphy is relatively passive. Wobbuffet doesn't command half the terror he did in the DPPt test. I've avoided him thus far by simply ensuring almost all of my Pokemon are fast enough to outspeed a Wobbuffet and therefore are able to use an offensive move on the Encore. I've lost a few slower walls to Wobbuffet, but not in a way that feels gamebreaking, simply in the same inevitable way that a Skarm would go down to a Magneton in ADV. Latios can put an immediate amount of pressure on, but I find the whole Draco Meteor, retreat, Draco Meteor, retreat thing to be fairly predictable, and playing around it is not too huge a difficulty. Deoxys-D just isn't really that good, I can't see it being BL, never mind OU. Tends to get shut down quite easily by Erufuun. Deoxys-S is a tricksy bugger, but again, fears Erufuun and isn't half as good as his DPPt days. Deoxys-A and Deoxys are totally shut down by priority attacks, they're the ultimate glass cannons. But yeah, I've not had problems with any of the other nominees.