Facebook now allows username change... once.
24 Jul 2009
I really don’t understand why facebook is being so stubborn on restricting username changes. It just creates frustration for it’s users. The only reason why they would discourage changes is to prevent you from breaking your own vanity url, or someone else taking your vanity url after you change it. Come on, facebook! Give your users a bit more credit. Don’t treat them like idiots. Explain the downsides of changing their username, then let them do it!
(more info: readwriteweb)