I'm not using rvm but I have ruby 1.9.2 in /usr/local/bin and stock
ruby 1.8.7 in /usr/bin.
I have /usr/local/bin before /usr/bin in my .bash_profile and /usr/bin
before /usr/local/bin in TextMate's PATH shell variable.
/usr/bin/env ruby is then /usr/bin in TM and /usr/local/bin in bash
For my scripts, I choose which version to use with the shebang. In
commands, if I want to be able to use both versions, I use TM_RUBY and
change it when needed.
I don't know if it's the best way to do this, but it works.
If there is a better way, I'd like to know it.