In order for the Map location to work on a Wi-Fi only iPad you must have an internet connection, and at least one of the networks your iPad can see must be in Apple's location database. That makes it a bit unreliable in sparsely populated areas.
Also, at the top of the map is a little arrow icon. If it is gray, the map is not in localize mode. Tap the arrow. When it turns blue it should center the map and locate you. Tap it gain and it points up with a little blue fan in front of it. This gives your your location and heading (the map points the same way you do). If you are near too much metal it will complain about compass interference, so that feature works poorly in a vehicle.
Edit: Apparently in iOS 5 the arrow turns purple, not blue. Hm.
