I'd like to know how mature the llvm-backend for Scala currently is and whether it is used in any open source project that I could have a look at.
I would say (sadly) it's pretty immature. You need certain steps among them: a scala standard library without java dependencies and a runtime including garbage collection. Which are still TODO. From my incomplete view on the topic I would say there is more to be done than what's already done. Check this for more info: http://vimeo.com/28774096