I think a great way to build the imgur community would be to add badges or buttons etc. to user profiles, awarded when users complete certain tasks.
I thought of a few examples:
Newbie - uploaded your first image to imgur
Whack-a-Mole - downvoted ten 1 vote posts to 0
Butterfly Effect - Upvoted a 0 vote post to 1, which then went on to get over 1000 upvotes
Curator - Upvoted a hundred images
Philanthropist - Upvoted a hundred comments
Downvote Fairy - Downvoted a hundred comments
Forever Alone - Maintained negative reputation for a week
...the list could go on. Each badge would have a little icon and would be displayed on your user profile once awarded.
Sorry if this is a bit outside of scope for Imgur, and I also realise this would have performance implications on the server farm, but it just occured to me while I was thinking about user rep. I think it would encourage people to get positively involved more and would give other users a quick idea of what you're like from looking at your profile.