I had that same concern. I bought a skin protector that goes over the entire phone. You can't even tell that it is covered because it is clear. I ordered one from Bodyguardz. The company claims that it is a scratch-proof transparent skin designed to custom fit the G1.
http://www.bodyguardz.com/
You can also check out ZAGG' s invisibleSHIELD
http://www.zagg.com/ as well.