"Other" files eating up my HD

After upgrading to Lion, I liked the new system information section, the stoarge tab shows you a graphic view of your HD, just like for iOS devices in iTunes.

I was surprised to know that 96 GBs are catigorized as "Other", what does that mean?? How can I delete them?

I visited to my Authorized Apple service provider and the guy said your only optoin is to backup your stuff, format the disk, then get going again.

What are your thoughts on this?? HELP!