BRETT4  On a new Penryn Macbook Pro with 2GB of ram, it took over TWENTY MINUTES to tag 10 photos from my 40D, and during those twenty minutes, the system was completely unusable- it took 30 seconds just to switch back to Safari, and it took two minutes to force-quit the program so I could get my computer back. I've never seen a program so completely monopolize a mac before, especially such a high-powered one.

40D photos show up incorrectly, with yellow backgrounds. Cities are not properly detected (it assumed I was in a major metropolitan city, not a suburb of said city, and did not offer any way to correct this except by hand-editing each photo. Since clicking on a photo means waiting a good 10-15 seconds while it calculates a preview, this is excruciating.)

Oh yeah, and the author appears linked to some sort of scammy "we'll give you the software for free if you sign up for this credit card/magazine subscription" website. Run away...  
(Version 1.5.4)

EJI  Wonderful app when used in conjunction with a Mac-compatiple GPS location device or a mapping app like Google Earth. I just used PGPSE to tag 200+ photos from a Paris trip using the coordinates from Google Earth, and it went smoothly. The coordinates appear in iPhoto's "Get Info" window and they can be used to map the shots in, say, Flickr for an interesting slideshow.

Best of all, PGPSE doesn't (as far as my testing goes) strip the other EXIF data from the photos.

v1.5 supports drag-and-drop, which was my only quibble with earlier versions. I don't really know how they could make it any easier.  
(Version 1.5)

HANGON  Great Great great....and the dev is very responsive to comment  
(Version 1.1.5)