Navizon already does this
Looks like Google stole this idea from Navizon who have been doing this on phones for years, even the iPhone.
http://www.navizon.com/
Google has begun testing a mobile phone mapping service which it promises will find your location and send you on your way, even if your handset’s not GPS-enabled. Dubbed My Location, the service initially requires you to download Google’s free Google Maps software onto your handset. Then, whenever you need to find a location …
I bought a Sanyo Katana DLX last weekend on Sprint and the new google thing doesn't find me. It seems to default to Minneapolis, MN. I happened to also get the paid-for sprint equivalent of the google thing, which seems to use the same technology(Navteq), and it can find me(with or without the GPS functionality, GPS seems to be required for routes though). Works for one of my co-workers T-mobile blackberry curve, another co-worker has a blackberry pearl(I think that's what it is), and the new google maps thing crashes his blackberry every time he tries to run it.
...sitting at home and it's about 20 yards (er...about 130 linguine) out. Plus it can give me directions to the pub along the road. Better get me coat, it's a bit nippy out tonight...
(Latest version of Google Maps under Windows Mobile 6 on a T-Mobile/HTC MDA Vario thingy, if anyone's interested)
In both my home and office, I'm getting my location within a "1,700m radius." That being said, despite Google using that disclaimer, the location that it's placed has has never been more than 600m away or so.
Still, given that I both live and work in Zone 1, London, a little disappointing. Unless this is just a reflection of how crap O2's network infrastructure is in the city.
At least I'm safe from the black helicopters...