When I came here, I was surprised to find that two things didn't exist: friends/contacts lists and visitor messages (vms). Others have addressed the friends list issue on this thread, so I'll just mention it. What I mean by vms is that they are the opposite of private messages (pms)- posts on someone's profile that are public to be seen. I used them in a 'this isn't important enough for a pm, so I'll use a vm' context. However, it's not something I miss that much.
Now, having used the site for a while (coming up on a year, I think!), I've decided that the private messages are... weird... First, it's almost like they open an entirely new thread, where I've previously used more of an email system. I prefer the latter, since they're simple to end the conversation by deleting. Second, there are certain pms with really long acronyms that somehow I'm invited to, but I can't leave. Sure, I can mute it, but I'd rather have the satasfaction of completely removing myself from the conversation. Maybe I'm still just a noob and I don't know how to do that.
So there's my wall of text to contribute... Not sure how much of this is actually capable of being changed or even will be changed, but you can have the input anyway.