Amazing example of what is to come, I can think of some great uses for this...
One question though, is it possible to allow users to define multiple custom options... what I mean is say I do the favourite colour instead of setting a few predefined colours to choose from the user is presented with a text field with the option of adding more text fields???
If this isn't possible by default is the custom userfields options extendible via php callbacks (and not just for validation)?