After a few days experience, I'm still very pleased with my iPad acquisition. Many have called it a huge iPod touch, but after the last few days, I think the iPhone/iPod touch is actually a small iPad.
While it is still early, I think we'll see a major difference between the apps available for the iPhone/iPod and the iPad. On the smaller form factor devices, there is limited display space and more of a need for immediacy - user wants to start an app, get the info they need, and get out. Great for a phone.
I think the iPad will prove to be a more casual device. What brought this to mind for me was after looking for an official Facebook app for the iPad. After searching for a few minutes, it hit me - duh! - open Safari, go to www.facebook.com, and login. There's not really a need for a Facebook app.
The web browser really is so good that apps that are essentially scaled down versions of websites for the iPhone/iPod don't need apps for the iPad. If you don't need an app on a desktop PC - you probably don't need one on the iPad. The main exception - so far - seems to be video, but as more sites adopt HTML5 and H.264, even those apps will be unneeded.
Where iPad apps really have a chance to shine are offline content reading, highly interactive user interfaces (see Google Maps), and games. Now that developers have a chance to see their apps on actual iPads, not simulators, we will see some very innovative new applications.