Using Active Social vanity URLs it would only display the vanity name the user selected, instead of their user ID. Example:
http://www.activesocial.com/users/ben However, it really just depends on how you secure your pages. If you have all your permissions set to "everyone" then, yes anyone can just browse the pages and get available information. The profile Info tab is set to friends only by default, and that is the tab with the most personal information.