Although I've only dealt with them for a fraction of my forum life, it'd be pretty hard to go on without our amazing profiles and vms. It makes it so easy to talk to people. Before, I'd find myself loaded with pms that were a pain to delete and find again, but the voice messages make it easy to communicate. To make a kind of a shaky comparison, it's like a new child in a household. Once they're there, it's hard to imagine what life was like without them. ^^
Who's online, custom avatars, and disabled smilies are pretty important too though.