For standard projects
Check in .ruby-version if your project depends on a ruby like ruby-2.0.0.
Check in .ruby-gemset only if your team agreed on it.
Add .rvmrc to .gitignore so anyone can override .ruby-* files settings with .rvmrc.
For gems
Check in .ruby-version with ruby-1.8.7 only if your project still targets ruby 1.8.7, otherwise check it in only if your gem requires it.
Do not check in .ruby-gemset.