1. It wears out the clutch much quicker and puts some wear and tear ont he transmission as well. If you don;t do this very often, you should be ok. Also, when you are peeling out and whatnot, if you keep the RPMS close to redline, or any kind high rpms constantly, that will put some extra wear on the motor.
2. Powershifting will mess up your trans very quickly, as well with your clutch. You can't say its the same as neutral dropping in an auto cause its different, but both will put wear and tear on the trans.