The thing I love most about these kind of apps, is that you can crack them out in a day - from idea to full functionality. It's instant gratification compared to some of the longer term projects I'm working on, and it gives me a nice break from them :-)
The reason ruby is so great for writing things like this is that it's so easy to extend. Writing ruby C modules is easy to do, so there's no real barrier - you write a little C module to do the tricky low level stuff, and manipulate that module from a higher level in ruby. Writing extensions for most other languages is complex and tedious in comparison (for me :-))
Having a lot of fun playing with bluetooth and thinking of interesting ways to use it - I just wish the bluez implementation had better docs..