I managed to set the username field in account matainance to ReadOnly but I'm (not admin account) still able to change his username :-[
I think the lastest nighty build still has this error?
Confirmed in rev 1070.
All fields are effected by this bug.
Q&T note; tracker URL http://dev.virtuemart.net/cb/proj/tracker/itemDetails.do?task_id=1578