When you have no username supplied, and attempt to commit, then the error message tells you so. But you cannot use --username as an argument, you must use --user. Why is there a difference here? I can understand not removing --user, but it would be useful to have --username as an alias to --user.
Duplicate
--- Bug imported by bugzilla@serpentine.com 2012-05-12 09:27 EDT --- This bug was previously known as _bug_ 3199 at http://mercurial.selenic.com/bts/issue3199