I've yet to use an iPad, but I've been thinking about how it will be received. In my mind, there are four groups that will make the iPad a huge hit: Mobile professionals, typical computer users, students and developers.
The first two groups -- mobile professionals and typical users -- will use the iPad as a laptop replacement. I think about the work that I do. Honestly, I only need my laptop when I'm writing posts. For the past few years, I've been successfully using my iPhone as a laptop replacement. Forget that it's even a phone for a minute. I'm able to communicate with my co-workers easily and rapidly via email, Twitter, text and instant message. Basically, everything I must do for work (save posting) can be accomplished with the iPhone.
The iPad will fill that role even more successfully as blogging becomes possible. Plus it's got additional screen size, battery life and connectivity. I think that many people will find that to be the case. Which brings me to group number two.
Typical computer users
Consider what the typical user does with his/her computer -- email, Internet browsing, photos, video (TV and movies). I don't mean the geeks like you and me, I mean our parents, sisters, brothers, aunts and uncles. Joe Shmoe. For these folks, an iPad is perfect. Most folks don't do involved photo editing with software like Photoshop, video editing, coding, etc. With the iPad, Apple has demonstrated that you needn't spend $1,000 for a portable computer. A portable computer, mind you, with 10 hours of battery life, extreme portability and dead-simple operation.
I see iPads resting on coffee tables next to the remote controls, just another leisure device ready for use. For many, the iPad will be their primary or only computer. And they'll love it.