Well also outgoing calls can (optionally) be routed through Google Voice. On my G1 with Google Voice, I have it set to ask me for each number I dial whether I want to use T-Mobile or Google Voice for the call.

I think it is fair to say that it alters the user experience of one of the core features (i.e. dialing a number). I just don't think that should be grounds for rejecting an app.