I posted a nearly duplicate comment (now deleted). My iPad has successfully located me in the Maps application in several different places. It's actually quite accurate.
Nice feature, pretty useless, though.
So it's got a cache of nearby access points it can use for positioning even without a network connection.
About 4 blocks away, it mistakenly placed me on a hillside 4 blocks in the opposite direction from my starting point -- but the local topography makes it very possible it caught a momentary signal from a faraway access point still in its cache.
From that point on, it provided no additional updates to my location -- even though I was following a 'directions' route previously called up, stepped through, and zoomed-on. From this I conclude: it precaches Wifi points near where you are when initially using location, but not along planned paths or all map areas viewed.