There a a lot of apps that will just use GPS if it is on. even the camera will use it to put location data in the image. google uses it for buzz, maps, latitude, etc. And if you have latitude, it will fire up every once in a while to report your location (which if you have latitude, you told it to do :)). there are some applications that will even use the GPS, if it's available, to show you "local" advertisements.
If you "opt'd in" for the "providing google with location information" when you set up your device, the device itself will use it to notify google about wifi locations and cell towers around your location. This data helps start GPS from a cold start, so it can lock on to a location quicker.
This data is good, and helps people that actually use the GPS. They are not "tracking your every move" like some people seem to think. Google, and Apple for that matter, couldn't care less where you are, what they want to know is where the cell towers are so they can tell you where you are with their location applications more quickly.
If you are worried about what may be sending data, then the only "safe" option is to turn off GPS unless you are using it, and check the permissions of applications when you install them. If your "Cooking Recipes" application wants to use GPS, that you may want to worry a little, unless it is going to tell you how to get to the store to by the ingredients.