[AaronM]

From what I've heard (and it makes sense), removing the balance shafts, while slightly increasing horsepower, will seriously reduce engine life expectancy because of excessive vibration. There are a lot of things under the hood that don't like a lot of vibration and the few hp you'll pick up aren't worth the extra mechanical failures. There's a reason the factory put the balance shafts in there, and it wasn't just for ride comfort.

Aaron

EDIT: If you want the engine to spin more freely (which is what disconnecting the balance shafts would do), you're better off getting a lightened flywheel. No loss of smoothness and the same increase in the engine's ability to rev.