Before we get started, it should be noted that the tablets being mentioned in this article are the new breed of tablets (iPad), not the older ones that are basically a touch screen on a laptop.
As far as laptop vs. tablets on the market, tablets are still quite new to the tech world. So if you are considering purchasing a tablet, there probably won't be much to pick from yet. As far as functionality, tablets are currently less capable than laptops.
Typing on a tablet PC is not terrible, but it does have a learning curve to it. Because typing is done on the screen, you must look at the screen to type, as there are no physical keys to use as a guide. I suppose that one could master the art of tablet touch typing, and get a good knowledge of where each key is. But still, you won't break any speed records typing on a tablet.
Alternatively, tablets have the benefit of being touch screen, which most laptops and netbooks are not. This means that you can utilize the newest technologies such as gestures, multi touch, scroll zoom, etc., directly on screen.
If you are the book reading type, a tablet gives you the overall natural shape and form of a book. Thus, it makes for an ideal eBook reader/computer combo. A tablet really would be ideal for taking just about anywhere, even to your local coffee shop. It's more of a natural fit for situations like that. In the future, many tech experts are predicting that devices like tablet computers will eliminate the use of paper. Many publishers, such as the New York Times, are creating deals that will allow "email like" delivery of the newspaper to tablets.
With a tablet, there is no CD/DVD drive, no physical keyboard, limited screen viewability, limited storage capacity (currently), and several other limiting features. Some tablets are designed to run full versions of operating systems, and others (such as the new iPad), are designed with their own unique operating system. A downfall, and the reason why many people will not buy the iPad, is its lack of multi tasking.