#1 priority for me - responsiveness. "Make any template responsive" works well for me.
#2 a custom stylesheet via admin so that I don't have to log into my server.
#3 logical captcha (hate the reg. captcha) - Andrew P I believe
#4 friends can reply to status updates (I am using "dolphin twitter" by modzzz)
#5 tagging of other members (http://www.demozzz.ru/extensions/media/photo-tags-for-photos.html)
#6 Delete unconfirmed members
#7 Privacy and Terms of Use editor
#8 Site see more Injections
#9 EVO Wall
#10 Upcoming Birthdays