With the proviso that everyone that uses it has an iTunes account...tied to hardware... (which is the big spam killer.)
I could see it available to PCs if the PC allowed access to the Intel CPUID (forces users to enable if they want 'face'.)
Looks like a break even for us. 550 family plan + 2 tethered 5GB data plans = ~$200. 2 iPhones on the shared plan w/ 10GB ~$200. Lets me eat more data as my wife just sips for the most part...and she eats the lion's share of voice (went over the last 2 months to keep in touch with her aging mom.)
I'm a TomTom iPhone user. I'd love it if they integrated with the iOS map API so they could take advantage of the crowd sourcing abilities with their existing traffic re-routing. And map update pushes from the crowd sourcing...