Phil (Frumph) & I worked out another SocialPress plugin this week. This one allows you to change your author permalink across your WPMU install. I also tested it in WP 2.8.3 and it worked there as well. For WPMU I tested from version 2.7 through to pre-release 2.8.3.
Built into both WP and WPMU is an author permalink such as http://wpmututorials.com/author/ron/ which uses author.php in the theme if there is one. With this plugin you can change the /author/ to a permalink base of your choice (ex. /user/, /member/, /profile/).
Using this plugin and a custom author.php you can create an author profile page. The plugin in the download has a custom author permalink of /user/. To use a different base change the second line of code
to your preferred author permalink
which would then change the permalink to http://wpmututorials.com/profile/ron/.
Download the plugin: [download#10]