This plugin includes a number of functions having to do with extending user profiles.
First off, when a new user registers (especially via OpenID, if you use WP-OpenID) the plugin tries to automatically add some information about them (name, avatar, etc) if it can be discovered using web standards (such as XFN and hCard).
The plugin also adds a lot more profile fields to the user profile page and a tab for permissions. There is also a profile preview generated on the edit page.
Generating a profile to display to users is easy. Just add
<!--diso_profile(USERID/USERNAME)--> to a page or add
<?php echo diso_profile('USERID/USERNAME'); ?> to your template. The profile is marked up with web standards (hCard and rel=me) and it only displays fields to those who are allowed to see them (according to permissions settings and the blog’s blogroll).
The plugin also has a sidebar widget, for displaying your profile in the sidebar.
There is also an easy-to-use sidebar widget that displays avatars (and optionally names) of recently visiting users.
Download the plugin