[krapp]

Really, usernames only have to be unique within a single thread, don't they?

You could get away with something as simple as incremental ids in that case - user1, user2, etc.

[kctess5]

Yeah that was my reasoning. The salted hash would be an easy way to implement single-thread username consistency.

Edit: for better readability it could be further mapped into a table of human readable handles, similar to how Google does the "Anonymous Lemur" thing in gDocs.