Since the latest review for this application is from 2010 I thought I chime in here real quick. I have been using GPSPhotoLinker for over a year and it has always performed flawlessly for me (OS X 10.8.5).
The interface is not particularly pretty or shiny, but functional and easy to figure out. I had no experience with geotagging before I got GPSPhotoLinker, but the process is really straightforward (even for beginners) - load the GPS data, load the photos and press a button.
Most folks will probably only ever use the "Auto" mode, but I have found the "Manual" mode to be a great addition. I built a little database of the places I visit the most inside GPSPhotoLinker and now I can apply my tags manually to photos I didn't record data for, that's really convenient.
GPSPhotoLinker is a great little app that does exactly what it is supposed to do (and it's free!).
PS: I use my iPhone to record the GPS data when I'm out and about with my camera. The app I settled for is called "Geotag Photos Pro" and it automatically sends the data to Dropbox from where I load it into GPSPhotoLinker - I'm very happy with this setup :))