Stolen cache

Recently, my hard drive has gotten really full lately, down to around 1GB or less. I had gotten home, loaded up Google Earth, played around with it (TX-130 is going to be how long?) and then quit it. My MacBook alerted me that my hard disk had only around 200MB left. That's insane! What the heck is killing my disk space? I decided to clear the Google Earth cache, as it does store a pretty large amount of space on my disk. I cleared the cache on Google Earth after figuring out how...and the empty disk space shot up to 2GB. Wow.