I inherited ladysolly's old iPAD 1 when she upgraded, and I haven't used it much. Well, at all. But I was messing around with it today, and I've put all my maps onto Memory Map on it. I've already worked out how to put the cache info on it, so that means I now have a rather large and probably not very useful, GPS. Also, it will do Wherigo.
The problem with the iPhone 3 is that the GPS takes a long time to update; I think it updates once per minute or so. That's probably OK for some uses, but not for geocaching. I'll see if the iPAD 1 suffers from the same problem.