Is your rails app definitely hitting the same ruby binary that
running irb or your command-line ruby script? Almost sounds like
either you're hitting a second (or older) install that doesn't have
some of the libs you're trying to require, or else ruby's load paths
are getting jacked up somewhere along the way if the requires are in
fact failing in your rails app.
Also, you may want to check out the google_geocode library:
I've used it in essentially the same exact way you've described in
your blog post, as a before_save in my model, works wonderfully.
Looks like your method would work just as well, just thought I'd
point out an alternate solution.