Simply being able to drag and reorder the blocks would be good - the blocks should have a minimize function on them too so that the user could hide them if they desired - this is not a huge cod change - simply css / ajax.

As far as user customisation of blocks is concerned I'm currently writing a mod to add the datatype html to profile fields - this will also sanitize the content by allowing admins to whitelist commands.

With this mod installed you can provide a field in the profile where the see more user can add html to personalize the account. Or if you make it only editable by admins yuo can add a field for the user - It opens up a whole list of possibilities...

This is also the correct way of controlling html posted within user submitted profile fields - other mods simply remove the sanitization from profile fields to allow the user to post anything they wish - A huge security risk!!