+more accurate colors and no color shift with the viewing angle change. Pretty much the best type of LCD. Usually you find IPS in the best monitors, and I am not aware of any notebook with IPS screen.
The TN panels they're being compared against there are terrible, though. My Eee (which is otherwise fairly similar: a 10" display at 1024x600) looks fine at those angles.
I have seen laptops with displays that are that bad, but it's not the norm, but it doesn't make sense to use them as the basis for IPS-TN comparisons.
While I will never buy a screen that isn't IPS for my computer, I question the necessity of it in this device. IPS makes a great marketing point and will make it look really shiny during demos, but I think it is the wrong tech for this device for day to day use. If I had to choose between colour accuracy and battery life, I'd much rather have the battery life. It's not like I'm going to be editing photos for print on the iPad.
My guess is that the viewing angle was a deciding factor there. While on notebook you can adjust the screen so it is at useable angle this is not an option for a tablet with no support. IPS matrix gets rid of that problem.
I'm sure color accuracy and marketing have very little to do with it. If they could have gone with the cheaper LCD they would have, but it would have meant limited viewing angle, which would not have been acceptable.
The newest iMacs use the e-IPS style of IPS panels, which according to Wikipedia have a lower power consuption than previous generations of IPS, presumably are much cheaper to manufacture than the other types (or they wouldn't be in a $499 tablet), and still keep the other advantages of IPS vs TN (color accuracy and wide viewing angle).
Them being in the tablet gives hope that these IPS panels will eventually end up in the Macbook, MBAir, and MBPro.
The pro is that you can view it from just about any angle and it still looks great. Check out some of the images on the Apple website in the iPad gallery and you will see that even from an angle there is no color distortion as there is with most LCD screens.
