Ton Zylstra writes about an interesting Second Life experiment, wherein he removed his avatar's human shape in order to present as... a glowing orb:
As you might expect, people treated him differently. He lost the expectation of speech, for one.
At a different level, I wonder about this as a case of going against SL's expectations about bodies and body types. When we see a school of fish in a river, for example, do we check to see if there's a player's av in there?