Tagging another user
We should be able to tag another user like twitter or facebook and have a notification sent to them somehow that they've been mentioned in a post. People definitely don't have time to sit and read hella pages out of an ot thread or something along those lines. Have a notification system where you can choose if you want emails/pms/whatever. Link it with the mobile app, send push notifications and it will get people coming back to the website more often.