Wow i didn't even bother to read pass page 2 of this thread.  Not having anything against obi, but some of you are just bias for the fact that he is Obi.  Hell, c'mon be honest. I will tell why i feel some of these pokes are Uber and can't stay in OU.
 Manaphy-   Manaphy is Uber no doubt.  Manaphy is basically a tad bit slow Azelf with MUCH better defenses and can Tail Glow without the fear of Pursuit.  With Tail Glow/ Calm Mind, Rest, Surf, Grass Knot/ Ice Beam/ Rain Dance.  Not a lot can even switch in or wall it.  Hell a Surf under Rain With Life Orb, will 2hko any Blissey IIRC.  Kyogre ( who you are trying to move to OU dies to Grass Knot.  If someone dares to use Vaporeon, what the hell can Vaporeon do back to Manaphy, TOXIC? while i rest? lulz.  Manaphy shouldn't be allowed in OU.  Can make Rain Dance teams more popular sure, but will be broken in so many ways.
 Mew-  If Mew was to be allowed in OU, you may as well give Cresselia 8 move slots.  if Baton Pass was banned on Mew then it may be a shot.  But he can basically do anything to it's counters he wants to.  He can Bulk Up, to avoid Pursuit damage, and then RECOVER later.  Or Calm Mind to reduce Shadow Ball damage, then RECOVER later.  He is basically Cresselia with more Speed ( Doesn't fear Tyranitar Pursuit ) He has the option to set up and INSTANT recovery, while Cresselia has to have an 8 PP Moonlight, and with T-tar everywhere that sucks.  Rest Talk is basically Cresselia only option.
 Ho-oh- Choice Banded Sacred Fire hurts every poke, then with the burn rate, makes a 2hko even easier, especially if Sand is out to negate leftovers.  With it's defense's he can switch in on Megahorns and Close Combat, hit back hard with Sacred Fire.  Hell even Punishment on Calm Mind Cresselia isn't anything to laugh at, or Calm Mind Slowbro.  Even rocks who are physical attack based, get ruined by burn.  Everyone says Stealth Rock this, Stealth Rock that.  A good player who wants to use Ho-Oh really knows how to not keep Stealth Rock on the field.
 Palkia - Make it hold Life Orb or Leftovers, and he is fine by me in OU
 Dialga- Same as Palikia
 Darkrai- Fine in OU
 Deoxys-D- Fine in OU
 Kyogre- Wow, lets be honest, what stops Kyogre.  He can wall with Toxic  ( other bulky waters )  Make Manaphy the biggest threat in OU.  Thunder most counters for some Paralysis.  Calm Mind and sweep, if you think CM Cune was TOUGH, you must have no met Calm Mind Kyogre, especially with Thunder at it's disposal.  Only pokes to wall Surf/Thunder Kyogre would be Quagsire <_< and Shedninja.  Not all Kyogre run choice items, so trying to trap with Dugtrio would be risky.  Too Specs set can 2hko Blissey.  Scarf sets runs through teams after Blissey takes its defeat.
 Wobbuffet- Fine in OU
 Lugia- Fine in OU
		
		
	 
Wobbuffet now... What you going to do with one in OU? The only thing that can hurt it much is a critical hit from Weavile's night slash or Banded Weavile, Specs Gengar or a Banded Heracross.
Lugia is a Cresselia with Roost or Recover and Whirlwind... Just no. Same deal with 
Deoxys-D... It has recover. The only reason Cresselia is allowed is because that thing doesn't have that vast movepool like Deoxys-D and can only heal by Rest-Talk or the 8PP Moonlight. Deoxys-D can spread EVs towards its HP and Defense while Calm Mind on SDef and kill, or Bulk up while it EVs its SDef and kill physically. Not to mention it learns Superpower, which kills Blissey in like 2 hits after Bulk Ups. If in anyway or form it is damaged, it has Recover as well.
Palkia... Are you serious? Lustrous Orb + Rain Dance (Either the move or Kyogre, if that gets moved down) + STAB Surf = It will kill... It learns Flamethrower, Thunder(or -bolt), Lustrous Orb + STAB Spacial Rend, and a quite a large movepool. Even if you send out Blissey, that thing gets killed by Lustrous Orb boosting, Rain and STAB Aqua Tail.
Dialga can probably be moved down if you were to choose one of the two dragons since he's slower and gets killed by a mass earthquaker, but still has great stats and quite a lot of resistances. Give it Choice Scarf and it would still destroy half of the OU tier, but this thing is a much more lenient choice than Palkia, who indeed is a beast.
Darkrai is an anti-sleeping beauty. Thank god this is only a single battle, or else Dark Void would be horrendously pwning. 
Mew -- What you said.
Ho-Oh: Aerodactyl's Stone Edge easily kills it before it can even make an attack... It's 4X weak to ROCK. Stealth Rock takes away half of its health alone. It's no problem in OU as long you have a relative decent wall or Rock type Sweeper. 
Manaphy: Hippowdon & Tyranitar & Abomasnow prevents it to be an user of Free Rester. Even if in rain, Modest Jolteon with STAB 100% Accuracy Thunder kills Manaphy no problem. If Wobbuffet gets moved down, it can either Encore or Mirror Coat.
Kyogre is a pain in Uber already... Its SDef is decent, along with Supreme attacks. STAB Water Spout with full HP and Modest max SAtk in Rain gives out HUGE AMOUNT of damage. Mantines get zapped by Thunder while Blissey can get killed with Aqua Tail. If it holds a Lum Berry, it avoids any kind of status, allowing it to take down at least 1 Pokemon with Water Spout. Even if you switch out Hippowdon or Tyranitar for Sandstorm to cancel out the rain, the Sandstreamer will be taken down by this whale.
So in conclusion, Ho-Oh is the only thing that should be moved down; Dialga is shaky, but I think it should stay up there in Ubers... And its typing is wonderful.