I've been using OmniGrowl for quite a long time, and I do really miss it now when it's on a machine that's not installed. The developers have generally been pretty quick to address problems (though I haven't interacted with them directly), and it's otherwise been pretty unobtrusive. I would definitely recommend this. I haven't seen (at least in any recent version) problems with the preferences pane always coming up, it works as advertised. I haven't tried everything it can do, but I have tried the RSS feeds, weather, iTunes notifications, log notifications, SMART notifications, and iCal notifications, and all work just as they're supposed to.