No technical limits were hit. They have nearly the same feature set.
Geocoder's api feels a little bit more modern Geokit (rails3 vs 2). Having read the code for both, Geocoder was cleaner and would be easier to tweak if necessary.
So really it's just a preference: they do the same thing.
We're a nearly-funded startup creating a social platform for local communities and neighborhoods.
* Web Dev Intern: Will be working on a Ruby on Rails web app with some civic-minded Harvard students. Some programming experience nice, but not required. We will help you learn as needed.