I'm an iPad owner and I love my iPad, but I would recommend laptops.
I love my iPad because I don't have a cellphone or an iPod touch or a laptop, and it sort of works as a stand-in for all those devices. My kids can play a game on it, or watch a video, or listen to music or an audiobook if they're trapped in the minivan for 8 hours or waiting while I attend a meeting or something. I can use an app to send text messages. And I can do some basic computer-type stuff on it (simple photo editing, web browsing, very basic word processing). I pair it with a small bluetooth keyboard since my middle dd and I are the secretaries of a number of organizations, so we use it for taking minutes. We've used it as a digital photo display for organizational presentations. I use it when I'm teaching violin in the basement of my home to quickly show my students musical performances that I think they should be familiar with.
But ... if I had a cellphone or an iPod touch, or if I had a laptop, the iPad would be an expensive redundancy which really wouldn't do anything as well as the other more specific devices. The lack of a keyboard is a definite drawback for basic computer tasks (unless you want to buy one, which increases the cost further and reduces the portability). The computer power and amount of storage is minimal. It doesn't have the ability to print or to share files directly (i.e. you can't plug in a thumb drive to copy files off to give to a friend or teacher, and to print you have to do a relatively complex business of exporting them in a portable format, syncing through iTunes, selecting files to share, placing them in a specific location on the syncing computer, opening them and then printing.
My two oldest kids (18 and 15) have bought themselves laptops. My 13-year-old plans to do the same once she has enough cash. Despite being familiar with my iPad and its capabilities they definitely wanted more computing capabilities than the iPad offered. The portability hasn't been an issue that they were willing to pay more and get less computer for.