I bought mine(over the other choices) mainly for the application support and sheer number of good apps. Im not an Apple "guy" per say and I still question some of the policies and OS lockdowns that they Apple adheres to. However, thats a small price to pay for stability, support, and incredibly diverse app market. Thats why I "got in". I looked at all the others and it didnt take long for me to come back to the iPad 2.
Its been a terriric device - reliable, amazing battery life, super-slick interface, etc, etc.
Thats my story.
As for what types of people use iPads, thats a tough question to answer since Ive seen or know all kinds of people that use them. Everyone from some of my hyper-nerd friends all the way to their parents or total NON-nerds. Young, old, male , female, black, white, green, red, etc, etc. Doesnt seem to matter! If you are trying to nail down a demographic of ipad users you might find it a very hard task!