James Stewart maintains a terrific blog that enumerates the particular differences between the many Rails plugins that interface with Google Maps and Yahoo! Maps (both for showing the maps, and for doing distance calculations, etc.). On his blog he refers to an “updated comparison” of all the plugins that exists on the “foss4r wiki.” However, the link he gives has been dead for awhile. I found the cached version on Google and thought others might find it helpful to put it online here on a site that exists. It ain’t the most beautiful table you’ll ever see, but if you’re doing geolocating with your Rails app, it is one of the most useful ones (click to see the full-size version).
I’ve been using Geokit and YM4R, but have been disappointed that as yet I haven’t been able to find a way to get Geokit to look up distance using a through clause, that is, it looks like any model that you want to do a distance lookup on needs to be “acts_as_mappable” itself. This is a bummer, since we have at least three models that will all need to store the same [lat, lng] coordinates if I’m not wrong about this. Not very DRY, but for the most part, it is a very functional, easy to setup, and extremely well documented plugin that I would recommend.