+1 on what Brad said.
Running anything without an exhaust manifold or header will cause you to float a valve.
LOL, did you just make this up? Let me guess he is going to bend a valve because of the cold fresh air hitting his hot valve!!!!
O.P.
No, its not good for you motor, in fact its relativly bad, but dont listen to the guys telling you its going to bend a valve or "float" a valve. In all reality the chances of real damage occuring if you are very careful (low rpm, low idle, low load) are pretty minimal, however as others have stated if your asking the question than you are worried, and a buddy and a pick up truck are cheap insurance for your bike and your piece of mind.