This post was originally posted on SharePoint 365, which has since been retired.
SharePoint 2007 had this great little link when you were viewing permissions and groups called All People. This would give you a full list of all people who have logged into your site collection, including any sub sites. This was a fast an easy way to see all people, and find someone to modify their profile.
NOTE I said “logged into your system”, not who has access to your system. If an Active Directory group has permission to your site, the users don’t automatically appear. They have permission, but until they first log into SharePoint, they won’t appear.
SharePoint 2010 has lost this useful link. Fortunately, it’s rather painless to get there. Go to any group, and note the URL in the browser
Change the MembershipGroupID value to 0, and hit enter.
The page will reload and show you All People!
Another neat trick, click Settings menu and you can modify the view to include more details, like their login name and email address. Now you have a full list of all users, along with their details.