It really depends on how many routers are in your area. For places in cities, there are tons and tons of routers so its very easy to get pretty good resolution. For places more remote, you might not see many routers and then you would be for more limited in your resolution.
Assuming you wanted to very precisely map a small area (50mx50m or so) to the maximum resolution possible, and you had a budget sufficient to buy and place 20 or so wifi routers, what sort of resolution could you get?
I'm looking at this for gaming applications. Don't need milimeter accuracy but +- 30cm would be good.
It really depends on how many routers are in your area. For places in cities, there are tons and tons of routers so its very easy to get pretty good resolution. For places more remote, you might not see many routers and then you would be for more limited in your resolution.