Yehuda Katz has a nice post over at his blog talking about Ruby 1.9 and what we need to do to move our community towards it.
Lots of great points are brought up, but for me, the biggest issue is just not having the time to fiddle with things, setup nice little aliases, etc. Thankfully, one of the nice guys over at Relevance has done this for us: spicy-config
On a quick side note, Chad's configs also helped me get up and running with zsh, and that's been a whole other fun trip.
You'll want to clone his repo and take a look in at his .zshrc file along with the ruby_installer and ruby_switcher files inside .zsh. All you have to do is source the files to get the functions defined, and run what you're interested in. I did set things up a little different given that I don't use the Leopard install of ruby...but if you're reading this, I assume you can see what you'd want to change if need be.
That's about it. I can now say "use_ruby_191" and it quickly switches me over, and then 'use_ruby' to jump back to 1.8.6.
Great stuff Chad, thanks!