accuracy is not the only thing (Score 1)

yes, 20-40m sounds really bad compared to GPS, but different applications need different accuracy. Imagine how many applications can do well with 1 mile accuracy location system, e.g. http://local.google.com/ uses your zip code and it works well. Currently our computers/laptops have almost no sense of location at all, and if Wi-Fi provides a cheap way to do location and enables cool applications, why not?
I co-authored a paper discussing various issues in such a WPS system. One of our conclusion is that AP moves/turnovers have slight impact on accuracy http://ramp.ucsd.edu/~ycheng/pubs/mobisys05placela b.pdf