I believe that the Apple iPad represents the next step in the future of computing. A trite and often spoken phrase, but let me explain.
Right now, laptops, phones and pdas are all viewed as tools. When I want to do something "online", I go looking for my computer. The future is when using a computer or getting on the internet becomes as frequent and often as watching TV, listening to the radio or opening my fridge. It needs to become a thing that is a given, always there, always available and everyone has one. The iPad changes this by bring a computer within price range of the all Americans. This is said with the assumption that after the first year of release the price will half, like most other technical products.
The iPad also lowers the barrier to use. Humans have an odd trait that 80% of the time we will use the tool easiest available or soonest available rather than the best tool for the job. What ever tool has the least barrier to usage, becomes the one we use by choice.
Today, when I want to get online I have to go "find" and "turn on" a computer. Even if that action is as simple as opening a device and logging in. The iPad takes another step toward changing this. Here is a device that is always on, doesn't have to be "opened" and is more "available" then other internet connected device. (Excluding smart phones). It's light enough and small enough that I can leave it anywhere, my bed, the bathroom, the kitchen, the car...it can just be with me as I roam my life.
Removing the keyboard as an essential part of the computer experience is a huge step. Apple started it with the iPhone and if they can truly enable keyboard less computing, it will dynamically change the way we use computers.
A note, I think netbooks set the stage for the iPad but I never felt that they were really the next step, they made computers cheaper but at the cost of quality. A good thing, but not necessarily an advancement in technology.