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.
Students (if the textbook publishers get on board)
We can't ignore the iPad as an e-reader. These devices have existed for a long time, but only gained wide popularity with the relatively recent release of Amazon's Kindle and Barnes & Noble's Nook. Of course, the iPad has the iBooks app and iBookstore. So what's its distinct advantage?
It's this: Whoever does textbooks right will win the e-book market, and Apple is very close. Here's why.
Students are on a fixed budget, and e-books are typically cheaper than their paper-based counterparts. Also, consider all of the money publishers lose when students buy used books from the campus bookstores. Additionally, Apple can distribute textbooks through iTunes U -- an established and proven system that students, faculty and staff already know how to use.
Suddenly the iPad is a device that follows a student from his/her freshman year of high school all the way through graduate school. Why buy a laptop when every student has a device that can be a textbook, reference tool, Internet appliance and whatever else the imaginations of developers can dream up? And that brings us to group number four.
When Steve Jobs introduced the iPhone, he specifically said, "The killer app is making calls." So what's the iPad's killer app?
The killer app is whatever the developers dream up for it. As John Gruber said this afternoon, Apple is essentially handing developers a blank slate and saying, "Go ahead. Make something awesome." In their hands it will be made to do nearly limitless amazing things. Come back six months from now and you and I might have different answers to, "What's the killer app on the iPad?" but we will have an answer. That one app that makes our life easier/simpler/more fun.