Bust The Wind
Gust of Wind ranks as one of the most powerful and useful Trainers in the game. Very few Trainers have the versatility and usefulness of this Trainer. If you follow my made up rules of building a deck, this card is almost required.
On offense, this card is almost self explanatory. Use Gust on a Pokemon that has few hitpoints left. Boom, instant knockout and prevents any chance of recovery with Gold Berry or the like. Use it to send in Basic forms of very dangerous Pokemon like Gyrados. If you are currently winning and you see Magikarp go down, Gust and kill before Fighting resistant Gyrados gets a chance to evolve. Same goes with other Pokemon like Totodile/Feraligatr and Squirtle/Blastoise.
Also on offense, use Gust to create mismatches against your opponent. If you have Kadabra out, Gust in Psychic-weak Hitmonchan and knock him out in one shot. This is most effective against Pokemon with high retreat costs. For example, use Gust on Kangaskhan if you have a Fighting Pokemon out.
Sometimes you are behind in a game and you need to stall. Gust Of Wind is also ideal as Defense. Gust in a Pokemon with high retreat that can't deal any damage in the next few rounds. I typically Gust in Articuno or Zapdos whenever I see it, because it takes two to retreat, but 3+ energies to attack. So the opponent must decide to either retreat with the Pokemon, or try to fight. Either way, you'll have at least a two round head start.
On defense you can also use it to create mismatches. With Scyther up, I might Gust in Hitmonchan and stall. If Hitmonchan retreats, then retreat Scyther and react accordingly, since Scyther has Free Retreat. This is a typical "dancing" strategy that's used to annoy the opponent, and most of the time it's quite effective.
If you're playing against a friendly person you know, here's a nice trick to play on them. Occasionally there comes a point when you must use Professor Oak and lose two Gust of Winds. Well, first Gust in one of their heavily evolved Pokemons with lots of energy, then use your second Gust on the Pokemon you actually wanted to use it on. Making them switch piles of cards can be slightly annoying. =)
Anyway, Gust of Wind is incredibly useful. I would have to say it's one of the more powerful Trainers. Around 2 to 4 in every deck is a good number.