One of the best uses I have seen on ipad are the comic books. I have been a fan of comic books, but I never wanted to pay for them, so I have not collected or read that many. Ipad is a perfect comic book reader. Marvel has digital subscription that allows you for $60 a year to have access to their library. But that is only available on a regular computer, not on the ipad. (This is because of a lack of flash support by the ipad.)
On the ipad you have to buy the invidiual comics, which puts me right back at not wanting to spend money on a 25-30 page comic book. Most of them are $0.99-1.99, but I have a hard time justifying to pay for 5 to 10 minutes of entertainment. I might re-read a couple of the comic books, but I just have a hard time justifying the cost.
Here is a review of the Marvel Comic book app on ipad so you can see how it really works. (It was originally on BoingBoing, not my own review.)
If only Marvel, or someone else, will set up a reasonable cost subscription service, I will be there.