Oh I will show you at some point soon just how easy it is to extract data based on last logged in time. I will also add some results to my Mini-Stats plugin.
Unlike the Simple Onlinelist and my Mini-Track plugin, this plugin actually inserts into the real user-meta the last login date which makes it easy to access.
Any where a user is loaded by bbpress, you now have the variable available $user->last_online (the $user part may vary but the concept is the same)
It's really almost as simple as this:
echo "$user->user_login was last online
<span title='".date('r',$user->last_online)."'>".bb_since($user->last_online,1)."</span> ago";
(the span and date is just to show an exact date when you mouse over the "xx days ago" part.
You'll be able to look at who has not been on in the longest time, who has been on recently, who has spent the most time online, and who has spent the least time online.
Unfortunately the user display list in the admin area is hard coded without filters and cannot be expanded with additional columns but it can be replaced by a new function.
I'll probably add the support to my "Mass Delete Users" which is useful to find members, even if you don't want to delete them.