I've been having similar issues today. The N800 was dead when I picked it up this afternoon (1300UTC 1/1/09), and when I gave it external power, it seemed to run with a high CPU load and became quite hot. I uninstalled omweather and mediabox, both of which had been recently updated, but the problem persisted across several reboots.

My problem didn't occur when I booted from internal flash, but reoccurred when booting from SD. It was running from the SD filesystem at the leapsecond increment. Eventually the problem went away and it now seems to be working OK.

This story on slashdot http://ask.slashdot.org/article.pl?sid=09/01/01/1930202 contains comments referring to issues with the 2.6.21 kernel and a leapsecond bug. People running fedora 8 have reported crashes. I'm not entirely convinced it is related, but perhaps it is.

Hopefully your problem goes away too, and hopefully mine doesn't come back.

fnord