This should interest apple laptop users (such as myself) as well as energy savers who shut down their boxes at night.This article is from Technofile, by Al Fasoldt :

"No computer system is without flaws. But I find it hard to understand how Apple, known for the care it takes in the design of both hardware and software, could have ignored a gigantic boo-boo in OS X.
The flaw is based on the way Unix and Linux systems typically clean up after themselves. Using a simple set of commands that are timed to run automatically every now and then, Unix and Linux computers get rid of junk files and do many other housekeeping tasks without requiring any user action.
Both Unix and Linux were engineered with the notion that their computers would be running around the clock. So it made sense to schedule a file cleanup operation at 3 a.m. each Wednesday, for example.
That's where Apple's humongous banana peel comes in. Apple's engineers slipped big time when they accepted the idea that Mac OS X computers would be turned on all the time -- or at least most of the time -- and would therefore be able to do their file cleanup at an ungodly hour of the morning once a week.
Bad idea. Very bad. Security is a nightmare. I've been telling everyone to turn off their computers when they're not using them. I realize this is mostly a Windows security problem, but there's no sense tempting fate. The safest networked computer is the one that isn't turned on.
And that means, of course, that Apple made a boo-boo that can mess up your Mac OS X computer big time. If temporary files keep building up, your Mac can run slower and even seem to be crashing. And, of course, you could run low on disk space in just a few months if you do a lot of printing or image editing. "

Mr.Fasoldt suggests two solutions:
a) run your machine around the clock for a week
b) download Macjanitor

Macjanitor is a great little program ( I use it ) That runs all the unix cleanup scripts at your leisure.It's only con is that it is a one trick pony,in that it only performs this task and nothing else.

You can download it here:

Hope I've helped