Unique at that moment in time.
Yes. Gather an initial DB and have it "self heal" as wireless signals change.
This is precisely what Google are doing with the combination of an initial street view drive followed by an army of android phones to keep the DB up-to-date. While every android phone continues to help update the database there is a good chance it will be very accurate.
I think it's a great idea, but not very novel. Google, Apple, Microsoft have implemented this and been using it for a long time.
The downside is that to get a location you need to be online to query the database.