Im having log in probs too, started in the last site update.
I have to log in at every visit, the log me in checkbox is ticked to auto log me in, but it just forgets about me :(. Its no real prob though just have to log myself in each visit.
The weird thing is that when I arrive at the site, sometimes my name appears at the bottom of the front page as if I am logged in allready, something is a little borked somewhere, no clue what it is though, cookies and Temp files have been cleared too.