Log out every day? Not going to happen.
One reason cited is:
So if you're logged in, cron doesn't run overnight tasks? Why not? Which tasks don't run?
I've been running Mac OS X full time since 2000, and I've never made it a habit to log out daily, or even "regularly". The number of times I've rebooted my Mac OS X computers is on the order of the number of times I've logged into my Mac OS X computers. When a program exhibits some "weird behavior", I would quit it and re-launch it.
The only time I log out is when something in Apple's WindowServer / CoreServices goes awry, or when I need to reboot, like for a kernel update. I think logging out every day to let your applications "start over" gives developers too much leash to write crappy software. I've had Firefox or Mail or NetBeans or Eclipse or iCal open for weeks at a time without restarting it. I expect software I use to perform reliably for at least that long without re-launching it. The only software I purposely quit as soon as I can are Microsoft Office apps and other apps that take up too much CPU/RAM when idle.
If I had to log out of Mac OS X every day I'd switch to Linux. If logging out lets cron run nightly tasks, then I think that's a bug (subject to me finding out which tasks won't run when I'm logged in), and I would much rather fix that bug than log out to work around it.
I won't dispute that logging out and in "cleans things up" and wouldn't hurt the reliability of your computer, but I will suggest that users should expect more of their computers. Windows users put up with crap like that, rebooting several times a day (though I'd hope it's not as bad now as it was 5 years ago), restarting apps regularly, putting up with crappy software, registry problems, spyware, viruses, swiss cheese security, etc. Mac OS X users should not put up with crap, period, especially not for the money Mac owners shell out for their computers compared to Windows boxes.