If you create a lot of serious artwork consider a larger model with more surface area. The smaller pads just don't allow you to make very broad strokes. This can really limit your style or sketching ability.
For people who just want to dabble, it is more than sufficient. Graphics, CAD, general computer use, the smaller surface area is probably more preferred. Less travel distance to move around the cursor and less room to take up workspace. The software helps to configure things as well. It is very accurate too, that's why I would like a second one at home. As AD stated, it is indeed a WACOM tablet.
Especially consider one of these if you have RSI or carpel tunnel. It's a great way to change your routine on the computer. It has helped my hands dramatically since I got mine a few months ago. At one point my hands were so bad I could barely make a fist and hardly had any grip strength. I had to stop gaming and cut down on the amount of design work I did. I have improved significantly since adding one of these at work and making some changes in my ergonomics and computer habits in my environments.
-baker