This window allows you to switch users, by tapping on the user's name. Each user has their own everything. Meaning, each user has their own Sessions, Bookmarks, Tags, History, and even cookies. This is an extremely useful ability, not just for sharing the iPad, but for separating profiles for single user devices; even when you don't need to share. Example: We use this feature to allow us to have a personal browsing user, and a user that stays logged into our support email account.
Each user stores his/her cookies. This allows you to literally have two different users stay "logged in" to multiple sites, while still keeping each user's information personal (and private). Example: User1 Logs into GMail, while User2 is logged in to Facebook. When you switch between users, the User1 will remain logged in to GMail, so when you switch back User2 you won't have to log in to Facebook again. This scenario is in use for our current email support. Users can also be assigned a password and permissions.