We already run a XMPP server for direct user notification.

I'm not familiar with Growl.fm, but I can say we're not at all ideologically opposed to using an open source web service. In general, we're looking for: - Good UI/install for end users - Minimal hassle to setup for us - Sensible authentication

When you think it's ready for primetime, shoot me an email (ben [at] fluther.com) and we can talk about setting something up.