Possible Duplicate:
Why does StackOverflow allow duplicate display names?
Is it really legal to have duplicate usernames? (This seems like an obvious enough question that I'm surprised I couldn't find it here...am I just missing it?)
On SO I went to users and searched for "Shawn"...and got a page full of users...all named "Shawn". Some of them with identical icons (but different reputation values.)
As a secondary question: is this a good idea? Could spoofing have detremental effects? And is there any reason to think that it's at all likely to happen? (As several people have mentioned, we don't really have any reason to think that this is an active problem at this point.)