Vim needs to be compiled with Ruby support for this to work. If you're on a Mac, the default installation of vim is -ruby, but it's possible to run MacVim (which does have Ruby support) in terminal if you want to.<p>Nice writeup though.
IMHO the use of an embedded interpreter really only pays off for plugins that perform a more or less complex task like parsing or something that requires functionality that VimL doesn't provide like internet access or interprocess communication etc. For simpler tasks, I'd suggest to stick with VimL.
Great. I've always wanted to write plugins. Would really appreciate if this could be followed up with a few more samples with some more functionality. Such as opening a small input window at the bottom for input and one for selection (as say in Command-T or fuzzy file finder).