I’ve been getting an intermittent problem with my Windows Live Messenger where it’d get confused about which contacts were online.  It’s been bugging me since the beta of MSN 8, but now it seems there’s a solution of sorts.  Check out this page: http://www.eggheadcafe.com/software/aspnet/28362799/re-xyz-is-not-in-your.aspx.  It seems if you sign out of WLM, then download and open this .REG file (at your own risk of course) your problem will magically go away…