Instantaneous values of location error range from 5 to 100+ meters on my N900. Typical values in the city 20-25 meters and more. Nonetheless I have no problems at all thanks to the OpenStreetMaps.
As said, Garmins have their problems as well. I saw people walking to and fro to find the right spot, and they claimed walking at 5 km/h helped getting more accuracy. Out in the open, with hardly any trees around. So we're doing quite well with the N900, IMO.