I don't know about Tauros, but Sceptile is fucking amazing and it would be a travesty to relegate it to relatively feeble UU company. That said, how do we define "too powerful for UU?" It can't simply be about what is available to counter said pokémon.
Just to follow along Obi's list:
Hariyama should easily stay in BL. It's always been very similar to Machamp, just Machamp is far more popular with the addition of No Guard. It still has essentially the same movepool and stats (with a couple oddball additions like Knock Off and Whirlwind) and Thick Fat gives it a very well-rounded set of resistances.
Sceptile... 120 base Speed Subseeding puts even the most bog standard team in fits and it still hits plenty hard since Subseeding in general absolves any need for defensive EVs. In UU, where defenses are generally weaker, it could really wreck havoc.
Jolteon is possibly too strong to move down. Gamebreaking Speed and T-Wave immunity (Volt Absorb is a damned good trait). The ability to Baton Pass makes it a bit unpredictable (plus untrappable) and it's still fairly strong offensively. Zapdos and Raikou don't exactly blow it away, it should stay in their company.
I'm iffy on Articuno and Venusaur but wouldn't be completely opposed to them moving down. Venusaur is pretty good but it's not significantly different from its Poison/Grass cousins like Obi said. Nobody's advocating Vileplume and Victreebel for BL. ;/ Articuno is good defensively-clerically but it is pretty unused and not overly powerful that we couldn't let some people enjoy it in UU instead of placing it in BL so nobody uses it anywhere.
Everything else I wouldn't have a problem moving down.
My suggested additions: Blaziken, Espeon, Floatzel, Moltres, Roserade, Umbreon, Zangoose, Magmortar. Infernape does everything Blaziken does but better, is Blaziken's similarily and additional versatility (Brave Bird, Endrev, can't it BP too?) why we want it in BL? Jump probably has his experience with Espeon and Floatzel as to why they're in the list. Moltres is in the same vein as Articuno; packs a whallop, sure, but completely one-dimensional, predictable, and still suffers from its typing. Roserade in the vein of Venusaur, except Venusaur can actually take a hit. ;/ Umbreon couldn't hurt Corsola any worse than it could Salamence, but it is too strong defensively to move down? Zangoose is just one of a hundred Normals with offensively-skewed stats; these days I think Ursaring is more dangerous than it. Magmortar is versatile, but its typing sucks and its stats are kinda goofy (too slow, huge SpA when most of its utility is physically-based).
Let's start making UU teams and battle each other then? Also, for OU, why not just take X-Acts suggestion and use only Pokemon that are in 5% or more of the ladder teams or Shoddy? That would place things like Tentacruel and Abomasnow in OU, of course.
Perhaps work on the number a bit, as per what X-Act says, but I think it's a good idea. It's against my personal philosophy, but most of us seem to be onboard with the "overused is based solely on usage" thing. The most logical way to follow through with that would be to, SURPRISE, base OU solely on usage. Follow the numbers...
Then we still have to decide which non-OU pokémon to move up to BL, which is basically what most of us are discussing now.
hi im mekkah also ban t-tar and garchomp
Touchy subject to be banning non-ubers, but anyway...
Garchomp is only broken because of Sand Veil, and thus only broken because of Sand Stream (which can also come from Hippowdon). Offensively, defensively, it's just a generally strong pokémon like a Metagross or a Salamence. The only real issue comes from the fact that oops, your Ice Beam just missed and Garchomp swept you. Using Substitute just exasperates the problem. But in lieu of making up stupid restrictions like "no Garchomp + T-Tar/Hippowdon" or modding the server (or, for now, asking Colin to do so on Shoddy) to remove Sand Veil, maybe Garchomp should be banned.
I don't think T-Tar is too powerful. I treat it much like Blissey. Is it a bit much that Blissey is such a strong catch-all special wall WITH recovery while already being a very good support unit and status absorber? It sure is. Strong enough that we've banned Blissey? Nope. In that same vein, T-Tar probably shouldn't have been given such a strong [special] defensive boost in addition to its previous strengths but it isn't strong enough to ban.