Not if you want it to spin well - lower BBs make things nicer if you're only going in straight lines as they're nice and stable, but if you want a flickier, twitchier (aka spinnier) bike, you'll be wanting a slightly higher BB. Not +65 or whatever, but if you look at BMXs and other bikes that are designed specifically to be good at hops, spins and tricks you'll see they've gotten progressively higher BBs over the past few years. Obviously street MTBs don't, but that's primarily because MTBing is always at least 3-4 years behind BMX
This was by Mark, just using Adam's computer at the mo