I keep my MBP running Lion pretty clean and lean with only files and programs that I need and use. Having said that, I had a 160 GB HD that had around 100 GB of "Other" that I just couldn't figure out what it was. I tried several different things over months and months and was finally able to figure out how to free up about 90% of that "Other". I went to the disk utility, selected the Macintosh HD and executed the "Verify Disk" function. It only took ~5 minutes to do and it said my disk needed to be repaired by restarting the computer and holding down the command and R key at the same time when the apple logo appears. This brought up a menu which would allow me to access the Disk Utility again and then perform the "Repair Disk" function. This again only took a few minutes and I was able to free up about 90 GB once I restarted the MBP after the Repair disk was complete. Not sure if this will produce the same outcome for you but it's worth a try and costs nothing.