I'd say Mega Pinsir is quite beastly, even if it's kind of predictable. Its basic set is Quick Attack, Return, Earthquake and Swords Dance, but I like running Close Combat for added aggression. You can run Hyper cutter to avoid a first-turn Intimidate, but I'd say Mold Breaker's the better ability due to getting through some Sturdy mons such as Magnezone.
Move wise I'd say the AI, who doesn't switch as often, probably won't give you that many opportunities to SD up without risking getting trampled over by an attack or status, and I think the added coverage is a welcome addition.
Like others and myself have said before, if you lead with Pinsir the AI will eventually metagame agaisnt it by running levitating ghost-types thinking they can void all its attacks, but that doesn't take into account that Mega Pinsir's aerilate changes Quick Attack and Return into flying-type moves. Other mons probably won't be as lucky and will be heavily metagamed against.
I chose to run Mega Pinsir over Mega Scizor in my gym team, and it has been a good choice so far. Scizor gets some added benefits, but you can reach a higher damage output with Life Orb (a lot more versatile and allows for Swords Dance) or Choice Band (raw power that allows for an extra coverage move). If you don't want to give Mega Scizor up, I don't think running regualr Pinsir would be a good idea, since Aerilate Return (and a QA that's almost as powerful as Technican Bullet Punch) is just that good.