It appears the issue discovered in this thread, is also a problem in ee 1.6.9:
http://ellislab.com/forums/viewthread/149815/
If auto log-in for future visits is checked, in Safari, the log out link doesn’t work, I just get redirected back the CP home and am still logged in.
In my testing, it appears, like the thread above, to only be a problem in Safari/Webkit, and only on sites that I’ve upgraded to 1.6.9. Older sites seem to work fine, even in Safari.