A problem we encounter in our small development team is that different Ruby on Rails projects use different versions of gems. Generally, most of our local development computers are up to date with the latest or close to the latest gem versions but, due to server constraints etc, a project is often lagging behind.
This means, when it's installed and setup locally, it doesn't run and throws a series of errors. We don't, of course, want to roll-back the version of a particular gem on each local development machine so it can be a bit tricky.
Another great article from Err the Blog gives what appears to be a very simple, robust and straightforward solution to this problem. Haven't fully tested it in-house but plan to do so this week.
Check it out: errtheblog.com/posts/50-vendor-everything