A lot of this discussion is bound to end up anchored in semantics.
The question is, at least in my mind, does the iPad perform a subset of mobile functions and provide the same or better experience due to its form factor then a desktop, laptop, or smartphone do? I don't expect to write a novel on an iPad. But it's not unreasonable to expect to be able to edit documents, view web content, and deliver audio and video on a device like this in a way that is superior to both a laptop and a smartphone.
I think that there are two ways of looking at this kind of device.
First, it's a fact that a large portion of laptop users, both consumers and business users, don't use laptops to the fullest of their ability. The appeal of the platform isn't so much its ability to be a jack of all trades device that is a desktop replacement (although certainly many users do have that need) but rather its mobility. Most users only use laptops at a fraction of their potential and mostly as a media delivery device. Laptops, despite their power, are constrained by a number of problems. Their form factor is unwieldy in many situations, requiring a table or for the user to be seated to type on, they aren't instant on, and they require physical media to install software which isn't always available when users are on the go (unless they carry their install DVD's with them- Unlikely).
And secondly, there are a large number of iPhone and other smartphone users who are, in fact, using their phones as computers. I would redefine the use of these phones as data communicators. People exchange and edit data on the fly on their phone in the way that people once used laptops exclusively to do. The obvious problem with smartphones is their screen size, battery life, and processor power.
Despite this, no one would argue that a smartphone should replace a laptop/desktop. Nor should the argument be made that a tablet should as well.
Tablets are the ideal form factor that properly designed would fit many of these functions. It can't replace a traditional computer in terms of text intensive tasks, but it has numerous advantages, particularly the way Apple has implemented it with the iPhone OS. Specifically, it's instant on, isn't unwieldy, has a GUI that is specifically designed for touch interaction, and has apps that can be installed easily, on the go, and without the need for physical media. And obviously, those who use their smartphones as computers should find a well designed tablet preferable to a laptop, which they may still prefer over a tablet when they're back at their desk.
What many observers erroneously confuse is the ability of a device to perform important functions for its users with the devices data input method. Some users will argue that since the iPad lacks a physical keyboard that it can't be a computer, despite the fact that many of the most common tasks on computers don't require intensive text entry. This is false. It also should serve as something users should be aware- If you need a mobile device for intensive text entry on the go the iPad is not for you. In fact, no tablet is. But that doesn't mean it's any less of a computer.
