Have a quad core desktop Windows system with dual monitors and a quad core 15" laptop, also with dual monitors when I'm at my desk. Need both for my work and my iPad cannot replace either one. That's especially true when I work with large spreadsheets and/or database applications.
Nor is the iPad sufficient for media when I compare it to either my desktop or my laptop with large monitors and a good set of speakers.
On the other hand, the iPad combined with a bluetooth keyboard and the Origami Workstation keyboard cover/iPad stand has replaced an 11" HP netbook I've used when I'm traveling for the last couple of years. (My desktop replacement laptop is simply too large to use when I'm crammed into a middle seat in coach.)
Thus, at least for me, the appropriate comparison is between a netbook (or perhaps an ultraportable laptop) and the iPad. Each has advantages.
() My iPad is lighter and easier to set up on a plane (even with the Apple Wireless keyboard) than my netbook.
() The battery life of the iPad is a godsend on a long flight. Any flight longer than 3 hours becomes dicey with the netbook unless I'm careful. (Some ultraportables are better on that score, but you pay for that technology.) I never have to worry about the iPad even with Bluetooth turned on.
() Interface. The iPad wins hands down. I hate trackpads so I'm forced to use a mouse with the netbook. Another object to fit on the tiny table at my seat in coach.
() I prefer the iPad's display even with its lower resolution to my netbook. The latter is better for spreadsheet work but only marginally so and the fact that I can put the iPad in either portrait or landscape makes it more flexible than my 1366x768 netbook display. So for email or word processing, the iPad wins.
() Keyboard. The netbook has a real keyboard. It's certainly better than the virtual keyboard on the iPad, but the Apple wireless keyboard is far superior to the rather cramped and less than stellar built-in netbook keyboard. Advantage: iPad w/ wireless keyboard. And if I don't need a keyboard I don't even pull it out of the bag.
() All in all, the fact that my netbook runs Windows7 simplifies access to Windows software, including Office. The iPad can use Documents To Go or Quick Office but each suffers from occasional compatibility issues with "genuine" Office documents. Fortunately, I don't have to rely on either the netbook or the iPad for serious work, but if I did, I'd have to give the netbook a plus.
() The fact that Windows 7 is a true multitasking OS and supports access to the file system is another netbook advantage. I still find it puzzling and frustrating to use the iPad as a "real" computer rather than a giant smartphone (without the phone.) On the other hand, booting the iPad takes seconds, not minutes. And again, I don't have to multitask much when I'm in the air and the iPad's limited multitasking is sufficient to listen to music while I answer emails or write a memo.
() My netbook has an external dvd player, an advantage if I want to grab a movie from the home library on the way out the door. But since the dvd player isn't built into the netbook, it takes up extra space on the tiny table in my coach seat. With the iPad I have to take the extra steps to convert and load a dvd into internal storage. Advantage to the netbook but not a dealbreaker.
() Cost. This is tricky. My netbook with a 360 gig hard disk and 2 gigs of memory was about $500 including the external DVD player. That's significantly less expensive than my $700 wifi only 64 gig iPad 2. On the other hand, a highly capable ultraportable with a SSD may run twice the price of the iPad. If I had to rely on a device for both the iPad's capabilities AND a full-fledged laptop, I definitely would not have purchased the iPad. But there simply isn't an ultraportable under $2000 that could compete with my 15" laptop. And even then, it doesn't measure up "specwise" to the laptop and it's not as portable as the iPad.
() Finally, there's one feature of the iPad that I haven't mentioned. I purchased it in part to share with my six year old daughter. She loves to play games and use it for the educational software I've added. On that score, no laptop can compete. And since I don't use the iPad for serious work, I can let her play to her heart's content without worry. In short, I can't "share" my laptop with my daughter, but I can share the iPad and that's a "priceless" advantage.
The bottom line is that some people may find an iPad to be an adequate laptop replacement. I don't. But it has so many unique features that it does fill a niche for me that no other device provides. And considering the drop in "netbook" sales and the softness of the "ultraportable" market, I'm apparently not alone.
