The tunes they sell for non-turbocharged gas engines are worthless.
I had BMW 535I with the turbocharged straight six and had a tuner on it that allowed more boost from the turbo, it was pretty impressive.
A good tuner on a diesel with the DPF delete as Dutch mentioned = Whoa Nellie!
On a naturally aspirated gas engine though, don't waste your money.
All of them will void your warranty if they're discovered, don't let anyone tell you otherwise.
