Some process is slowly taking over disk space...how do I find out what this is and how do I deal with it? I have a Mac Book Pro, first generation.  It is running 10.6.4.  I usually keep it running.  I put it into hibernation mode (i.e. it writes the state to disk and powers down) when I need to put it to sleep.

I have a ~100GB hard drive.  Now I only have about 3.5 GB free.  I've noticed that recently i get the low disk warning quite a bit and when I check sometimes it dwindles down to a few MB.  I figured that it might have been my browsers (Chrome, Safari) caching stuff. I clear the cache and it frees up some space.  But I never get back to 3.5GB.

So, I decide to shutdown and restart.  Every time I do that I see that indeed I get back to about 3.5GB free.

My question is how do I figure out what is slowly eating up my disk space?  Have people out there experienced these symptoms?  What was the cause and how did you deal with it?
It’s a combination of the page file (virtual memory) and the hibernation file that gets written when you put your computer to sleep. Of course, other processes may also leave temp files that get deleted when you restart. There isn’t really much you can do to improve that without affecting your computer’s performance. 

You can get a utility like WhatSize, Daisy Disk or similar to visually inspect the contents of your hard drive and see where is the “abnormal” file or directory. 

You can also use Monolingual to reduce the size of your executables and remove unwanted languages and files.

Update: 

The virtual memory file is located in 

/private/var/vm


and the hibernation/sleeping file in 

/var/vm/sleepimage


Please not that you can’t (and shouldn’t) delete the vm file while OS X is running.