my commute i only clean the drivetrain once every 2 weeks, or once a month if i'm lazy. my road bike i wipe down frame and drivetrain every 100-200miles.
by cleaning drivetrain i mean. filling up a chain cleaner halfway with simple green, and rest water. run the chain threw for a miniute or so. use a tooth brush to clean the cassette, jockey pullys and chain ring. rise out the chain cleaner and use water. run threw again, then wipe dry with a rag. after that i add chain lube and wipe it down once more with a dry rag.
my commute bike i don't care as much about, so long as the wheels roll and the chain works i am happy. my road bike i am a bit more anal about keeping nice. i hear babywipes are good for wiping down frame and other parts. make sure you wear plastic gloves and clothes you don't mind getting grease on.
http://www.jimlangley.net/wrench/cleandrivetrain.htm