That's a slightly inaccurate question: my computers are usually permanently logged in, but I generally hibernate them when I'm away. They're set to prompt for a password when restoring from hibernation, so I suppose technically I'm logging back in then.
Anyway, at work I have Outlook set to auto-run on startup. So first I'll go through that checking for any emails, check a couple other information pages for updates, then pick up the pieces of whatever bugfix or development I was in the middle of.
When I get home I usually hit LiveJournal, sign into IRC, check half-a-dozen webcomics, check the RSS feeds, check emails, and check a couple of forums I frequent. About half of that happens automatically, or should at least (the RSS reader appears to get mildly confused by hibernation, and fails to update half the feeds). After that it slows down a bit, and quite often after doing that I'll abandon the computer and fire up a games console (currently the Nintendo 64).