I have created a "user profile" gadget that has two functions:
1. If the logged in user has not populated their user page, it nags them with a notification.
2. If they visit their empty user page, they are presented with a form that will create sort of a bare minimum user profile. They can always manually edit the page later to refine it, but at least we get to know a little bit about the users.
3. Users can disable the nagging by visiting the Gadgets tab of their Preferences. (This may also speed up response for users that have completed their page by a mS or two. The gadget may become self-aware enough to disable itself in that case.)
Feedback (and refinements) welcome.