Users love using these applications on their phone or their MP3 player because it's like nothing they've had before on such devices and there are few alternative devices which offer this level of polish.
We won't see anywhere near the numbers of applications developed for iPad because people simply won't be buying it in the same volume as iPhone and iPod touch. There will be a much, much lesser incentive for developers to make applications for it and doing so will be much more challenging.
As it's running iPhone OS, it's probably going to have all of the huge memory problems that iPhone does and it's going to suffer from these same developers not knowing how to create solutions. I can almost tolerate the OS taking 10 seconds to free up memory on my phone after I quit something, but on a device which supposedly replaces my laptop this would be unacceptable.
Oh yeah, and does Apple REALLY expect people to boot up a different computer every time they want to print a document from iWork? Do they really expect people to type on this thing or use it at the crazy angle shown in the keynote yesterday?
I predict there are gonna be a lot of people complaining of tired arms on the day the first devices start arriving.