It appears that in the Ruby download, a configuration issue with Snow Leopard (OSX 10.6.x) causes the ability to use the standard input (‘gets’) to break. As long as you are running the script from the terminal then it will accept keyboard input appropriately, but using the CMD-R feature in TextMate does not.
There is a published fix that involves updating the interactive input library.
You can get the library here: (github). This needs to be placed into the
directory. I did this and voila!