A bizarre one that affects Microsoft DreamSpark, (and probably others) is that they silently escape characters in your password. Apparently they do this using two different methods depending on whether you're logging in or changing your password, so if it gets escaped one way, it might not be escaped the other way, and then you can't log in.

Consequently I don't think you can include brackets in your password if you want it to work. The front-end apparently isn't aware of this limitation, so they'll happily let you do it.

Code re-use: a very good idea.