This isn't much of a tip, per se, but it's something I ran into today.
The way to having multiple rubygem repositories is to set the GEM_PATH environmental variable. This will allow you to use gems from more than one location -- something useful on shared servers.
Next, to figure out how to specify the version of rubygems you're using -- I've tried GEM_HOME and RUBY_LIB and my PATH, but it's not working properly on the shared host. More once I figure that one out.
