I haven't experienced that since the first week of Beoir, when a setting was missing. Although it happened twice to me when I was rebulding my laptop (don't ask) and had accessed the first time, but now, now I'm automatically logged in every time.
It happened to some users on ICB, and seemed to be more a function of the browser (though both ICB and Beoir are a little "complicated" as the main site and forum are actually separate sites). You can try to purge your browser cache and try logging in from the front end from sctratch. Do you always check the remember me box?
Diablo, I can find out if there's a support issue with the sign on modules when it comes to Safari, but if there is, there's not much we can do about it (not home-grown code on those parts) other than report it ourselves. The logs show a few Safari users, but this hasn't been reported till now, so not sure if it is a common issue.