For RC30: The g1′s user-agent is:

Mozilla/5.0 (Linux; U; Android 1.0; en-us; dream) AppleWebKit/525.10+ (KHTML, like Gecko) Version/3.0.4 Mobile Safari/523.12.2

Update 05.31.09: Cupcake is listed as:

Mozilla/5.0 (Linux; U; Android 1.5; en-us; T-Mobile G1 Build/CRB43) AppleWebKit/528.5+ (KHTML, like Gecko) Version/3.1.2 Mobile Safari/525.20.1