I bought a Garman eTrex Legend about six or seven years ago, just because I thought it would be a neat toy. Found out about geocaching after I bought it, and took up the hobby. As a previous poster said, some of the caches are kind of lame, but many are really quite cool - well hidden, well camouflaged and insanely difficult to find. The "treasures" are usually little trinkets not worth anything, but the goal is to find the cache and sign the log, not to find a "treasure". Also, if you take something you leave something. Also, you don't bury the cache. No digging.
Also, you need to hide some caches of your own. It is cool to hear positive comments about how much people enjoyed the search for one of your hides.
Geocaching gets you outside, and I found many great places I never knew were there, in an area I've lived in for forty years. It's a lot of fun, even though I haven't done it for quite some time.