You won't smell a boost leak - it's just air. Unburnt fuel could be possible, especially if your car is tuned, however, you shouldn't really smell that while moving unless you have a rather large exhaust leak. First thing that actually comes to mind is clutch slip under hard acceleration. Maybe it's not slipping enough to really shoot the RPMs up, but could be just enough to get a little smell going.
How many miles on the car? Mods?