If you want a multi-million business based entirely on SemWeb Technology, try http://www.garlik.com/ (Nothing to do with me, by the way.)
I agree with others that looking for the Killer App is strange. It's the Killer Edge (business-wise), and possibly the Killer Business that matter. I know quite a few places that SemWeb Technologies are used to give businesses or consultancies an edge - it's no big deal for them; they just do it, and their customers don't even need to/want to know what technologies are being used, so why make a song and dance about it?
