First off, impostors are stupid and well, pointless.
Now, make a 1 letter difference between names not be allowed, then make it so small punctuation marks will not count as a difference in name: , . ' `

It's annoying to see someone impersonating someone:
Real:
Phoenix
Fake:
Phoenix.

i agree with SL...

most internet sites and groups, or even here at work, they dont let you use puncuation at ALL for your username.

the bad part now would be enforcing all the current users of puncuation to change their names...

though symbols are cool {}[]<>|\!@#$%^&*()

<> isn't allowed already, wicked easy to pose as someone with /me with it.

i will join the chorus.
although it is rarely difficult to verify whether it is the real McCoy or not, it is rather annoying.