Option to Sign On as a Certain Status
Signing on as Invisible is important to me in an IM client, because I often get online to talk to one person in particular at the time, and this option allows me to avoid having to explain that to other people who try to IM me. I know there are also plenty of people who like to sign on as Away, instead of Invisible, so a simple option like this would certainly please a lot of people and would not be needlessly complex.