this is my suggestion
on the profile page, under how many downvotes and upvotes you recieved, you could have something to show when you were last on the site? like this
Last Active: March 31, 2013
my reason for wanting this is for username changing purposes.
because i once heard you could steal someones username if they hadn't been active for 6 months, so this could really help people out if they want a username of someone else's