There's a geocaching site that let's you find caches in your area. I've done a few with my children during the summer. It's really fun and gives the kids something to do while you are hiking. Just remember to bring something to refill the cache. Oh, and sometimes the gps gets you close to the cache, but not exactly on it, so you have to do a bit of hunting (not that the kids minded...).
yepp, we geocache. it can be a lot of fun. Check out http://www.geocaching.com/ There are tons of cool treasure-hunting expeditions and you can create your own and get feedback from those who find it. addicting!
We haven't gone in a while, but we used to on a pretty regular basis. We have a couple caches we maintain and have containers with the intent to place more. I think it's great fun! The only tip I have is that often the metal base on light poles can lift up. That is a popular hiding spot and one that took us a while to figure out.
My husband and I don't get to do it often while we are on different schedules (he works nights), but yes! He introduced me to it, and we do it when we can. We have a lot of wilderness areas out here, and it's really fun to search for the one rock/branch/cactus to find it.