Geolocator is a Mac OS X application (made with Xcode and AppleScript) that simply displays the location of a photo in Google Earth.
This is a droplet, so you can drop a photo from Finder, iPhoto, or anywhere else onto the application's icon in the dock and it will instruct Google Earth (you must have this installed, of course) to fly to the location indicated by the GPS location in the EXIF data of the photo (this only works with photos that have somehow been tagged with this information already).
The AppleScript was based off a similar application developed by Craig Stanton named Geotagger, which does the opposite of Geolocator. Geotagger is a great, simple app that adds the current location in Google Earth as a GPS location in the EXIF data of a photo. I highly recommend it!
Stefan Geens of Ogle earth has made a set of crosshairs to help you zero in on the photo's location in Google Earth. The location at the center of the crosshairs is the exact location specified by the photo's GPS data.
The Exif handling code comes from exiftool. You can find out more about this very useful utility at the official webpagehttp://www.sno.phy.queensu.ca/~phil/exiftool/.
You can download Geolocator.app here. I've only tested it on my iMac running OS X Leopard, but I think it should work with any Mac capable of running Google Earth (version 4 or later).