I understand the afore mentioned, however, the point I am attempting to get across is that the computer is an 80g hard drive, it came with 56.90 free, and has since dropped, not adding any programs or applications. By browsing internet and Ichat, it loses hard-drive space. This should not be occurring. Correct me if I'm misguided.
That's not unusual at all. It will happen with any computer (Windows or Mac or Linux, etc.)
Browsing the Internet is essentially retrieving "files" from the Internet. Every image, every page of HTML, everything, is a file. And, when you go to a web page, you are retrieving those files for display on your screen (in the browser).
But, it doesn't stop there. Every one of those pages and it's files are also cached / copied to your hard drive so that your future visits to that same page load more quickly.
And, then there's the "cookies" that different sites store on your computer so that they can "remember" information about you and your previous visits to their site.
And, then there's the cache files on your computer that are created by different programs you use on your system (such as your word processor, e-mail program, etc.). Each of those takes space.
Then, there's the log and history files created by OS X to document what's it's done. And, of course, many other programs create these log files.
And, then there's the virtual memory that OS X creates (Windows will do this as well). The virtual memory is where information gets stored when your main memory is nearly full. It stores information you don't need at the moment on the drive to free up RAM for something you are actively doing.
The computer is always swapping information back and forth to this virtual memory file / swap file.
This file is kept on the computer and grows as needed. Once in a while it is purged and shrinks. But, it usually retains information for a while to use if it is needed again.
All this stuff and more can account for large amounts of space disappearing.
Right now I've got 35 GB of space being used by my swap file. My other systems with less memory will actually have even larger swap files.