>>... I did this with some locality data I had on a gravid South Florida Mole King from many years ago. I have a marker on the exact dirt road intersection that this snake was captured from, from a real satelite image to boot.
Can I make a pitch for taking geotagged photos at collection sites? You get a photo to remind you of the habitat, and a precise location (which incidentally can link with google earth to give you even more views of the location).
Big DSLRs can use external devices.
For compact cameras easy to always have at hand when you're in the field, the Nikon P6000 is the only choice. It can take a disappointingly long time, sometimes, to get a fix; Other times it gets a quick fix and adjusts it as you walk around. Mixed bag. It's been out almost a year and i keep hoping Nikon will improve the GPS technology, or that another maker--Canon, maybe--would bring out a competitive product. But so far, no go.
You can also use an Apple iPhone. With the phone's "Location Services" turned on, any pix you take with it will be tagged. The iPhone seems to get fixes reliably and in seconds, so it's puzzled me why the bigger-bodied P6000 can't match that performance. Of course, the iPhone pix aren't nearly the quality of the Nikon's. But they do have this nice feature: import them (or pix tagged using either of the other two methods described here) into Apple's iPhoto, and when you click on a little icon on the image viewer, the photo rolls over to reveal a map with the geotagged location marked by a pin. AND using iPhoto's "places" feature, you can see a map with ALL the tagged photos in your photo library: click on a location, and it'll take you to all those photos.
Lastly, you can use the iPhone and take a higher-quality photo at the same site at the same time with a better camera. You can then batch process images using software that matches the TIME the iPhone pix were taken--and tagged--and then transfers the tagging to the better-camera pix taken at the same time. A cool process, though it's an added step in the workflow.
I think there are some great tools here to enhance our observations. In fact I think i'll post this on the field collecting forum, too, though it might not be a new subject there.