My first thought was browser games but then I don't know if the I-Pad can do flash yet or not. I haven't been keeping up on it.

It does look like Seadragon might do what are talking about Torstan but whether it runs on the I-pad or not is another question. Someone here recently put a map up on that and it is pretty cool. I haven't yet read up on what all you have to do in order to use it though. They have like a Silverlight based version and a Java version or something.

For sure the I-pad would be easier to carry around than a laptop if you were going to go DM at a friends house.