Today I thought it might be handy to change my username on a new Lion MacBook air to match the nameing convention of my other Unix/Apple boxes, from "bert boerland" towards the more unix command line friendly "bertboerland".

Once I did that I left the machine running and after some time the screensaver kicked in. Then when I wanted to login on the OSX, there was only a box with my OLD username already filled in and room for my password. Sure enough entering the right password (with the non selectable old username) resulted in a wrong combination.

There was no other way to log in (other then via SSH) towards the box. Yes, I actually had to reboot the box to be able to login again!

You can prevent this by ticking the boxes under preferences > user management as shown below (in Dutch). But having this default is rather stupid Apple!