Generate default user account pictures
The default profile picture (or avatar) is bland and boring, and it doesn't help to differentiate user accounts. It would be great if we could replace this with colourful images featuring users' initials. Not only would these help to identify users, but they'd inject some much needed colour into the experience.
If we were to do this, the control center's user accounts panel would need to do the same thing. It might also be interesting to make the same facility available to apps (particularly contacts, mail, messaging).