I read that Diana had a similar problem earlier today. For a good number of weeks now, I've been logged off everytime I've come to MTF. And just for good measure, I'm also having trouble with pages that stall, which means I'm sometimes unable to access anything. No idea why this should be.
I was logged off suddenly all the time too, until I started ticking off the "Remember me"-box when logging in. Afterwards it was better. Have you tried that? Didn't help with today's troubles, though.