Tailwind: Doubles the Spe for 3 turns
So, Tailwind is pretty much an Agility or Rock Polish for 2 turns (one turn gets wasted upon activation).
Here is a list of usable Pokemon in the Ubers tier that can learn Tailwind:
Arceus - more of a sweeper, there are better moves for support sets
Giratina - not much space for a support move that won't benefit it
Giratina-O
Ho-oh
Latias
Latios - more of a sweeper (although Legends Never Die runs DD just for the speed boost)
Lugia
Mew - has better options (RP/BP, SR, Hypnosis, etc)
Rayquaza - has DD, not suppose to be a support poke
Scizor
Shaymin-S - too fragile to set it up, could set up LS on the switch
Zapdos - already has Agility(/BP), not too common in Ubers
So, in bold are some pokemons that I think can use Tailwind to a decent extent. But even if the +2 Spe is nice, the move is far from broken so let's talk about how would it be useful enough to be considered in a set.
Giratina-O has T-wave to cripple switch ins. However, RestTalk, Lumberry or Ground pokes don't mind it. Tailwind lets your Giratina-O be faster than most threats without losing 25% using a sub. You can even switch to a counter that would still benefit from one turn of +2 Spe.
Ho-oh was discussed a little in its own thread. As far as I know it is supposed to be under testing, although I recall battling against somebody that used it pretty well (I think it was Jibaku).
Latias is a support pokemon so it could use it. The thing is, Latias already has a lot of support moves (Wish, Roar, LS, Reflect, Safeguard, etc.) and most of the times it has Recover which takes away one moveslot.
Lugia also learns a variety of support moves (screens, whirlwind, status, etc.) and it has a form of recovery that takes away another moveslot.
Surprisingly enough I could see Scizor using Tailwind fairly well. He is not really a sweeper, he is more of a transition poke soaking up resisted attacks and forcing switches with U-Turn. Tailwind+U-turn on the switch (usually Scizor counter) could be viable. A 0 Spe EVs Scizor can outspeed positive nature 90 based pokemon like Kyogre and Dialga (most non-scarf versions don't even run Spe EVs) after Tailwind and even a non-scarf 252 Spe Timid Palkia (332 vs 328).
Like I said, this move is far from being broken or vital, but I'll leave it open for discussion. Some slow teams may benefit from just one Tailwind user even if it will require some skill to pull it off successfully.
So, Tailwind is pretty much an Agility or Rock Polish for 2 turns (one turn gets wasted upon activation).
Here is a list of usable Pokemon in the Ubers tier that can learn Tailwind:
Arceus - more of a sweeper, there are better moves for support sets
Giratina - not much space for a support move that won't benefit it
Giratina-O
Ho-oh
Latias
Latios - more of a sweeper (although Legends Never Die runs DD just for the speed boost)
Lugia
Mew - has better options (RP/BP, SR, Hypnosis, etc)
Rayquaza - has DD, not suppose to be a support poke
Scizor
Shaymin-S - too fragile to set it up, could set up LS on the switch
Zapdos - already has Agility(/BP), not too common in Ubers
So, in bold are some pokemons that I think can use Tailwind to a decent extent. But even if the +2 Spe is nice, the move is far from broken so let's talk about how would it be useful enough to be considered in a set.
Giratina-O has T-wave to cripple switch ins. However, RestTalk, Lumberry or Ground pokes don't mind it. Tailwind lets your Giratina-O be faster than most threats without losing 25% using a sub. You can even switch to a counter that would still benefit from one turn of +2 Spe.
Ho-oh was discussed a little in its own thread. As far as I know it is supposed to be under testing, although I recall battling against somebody that used it pretty well (I think it was Jibaku).
Latias is a support pokemon so it could use it. The thing is, Latias already has a lot of support moves (Wish, Roar, LS, Reflect, Safeguard, etc.) and most of the times it has Recover which takes away one moveslot.
Lugia also learns a variety of support moves (screens, whirlwind, status, etc.) and it has a form of recovery that takes away another moveslot.
Surprisingly enough I could see Scizor using Tailwind fairly well. He is not really a sweeper, he is more of a transition poke soaking up resisted attacks and forcing switches with U-Turn. Tailwind+U-turn on the switch (usually Scizor counter) could be viable. A 0 Spe EVs Scizor can outspeed positive nature 90 based pokemon like Kyogre and Dialga (most non-scarf versions don't even run Spe EVs) after Tailwind and even a non-scarf 252 Spe Timid Palkia (332 vs 328).
Like I said, this move is far from being broken or vital, but I'll leave it open for discussion. Some slow teams may benefit from just one Tailwind user even if it will require some skill to pull it off successfully.