Let me make it clear to Last.fm and every other website in existence: I haven’t the foggiest clue what your specific username requirements were when I registered, or whether I decided to use my first name, full name, moniker, or favorite Steinbeck character.  But I do remember something very well – the same email that I’ve used for the last 6 years.  Ask me for that for login credentials, and we’ll get along just fine.

Interaction Designers – I’m looking squarely at you.  This is our job.  In my opinion, a username is a completely invalid login requirement for all but the most fundamental credentials, such as your OS account, or for bank accounts (which can claim the “higher security” excuse).  What do you think?

— Update —

@salConigliaro points out, “At the very least let me use my email address as my username.”  While I agree, this also means that your publicly displayed username, assuming that’s why the user name exists in the first place, has to be your email address.  For both privacy and formatting concerns, this may be less than ideal.