"Do I need an iPad?" is not a good conversation starter. It's someone itching to buy one and use you as the excuse for spending up to $1,000
What it isn't.
Let's get it straight that an iPad is not a computer. In essence it's an iPod Touch with with a bigger screen. That's all. So really it's an extension of your computer. True, it can do most of the daily functions that you use your computer for: browsing, email, basic word processing, watching videos, listening to music, etc. The large screen just makes it a lot less pocketable and a lot more functional that the Touch. But the iPad can't function alone. Periodically you need to link up with your desktop and iTunes.
Can you justify buying one?
So could an iPad be considered at all practical? Sure and even more so I think the iPad will actually change the way we use computers. Here's what I mean: In a household of 4 people, you probably have 3-5 computers currently. Give everybody a $500 iPad to use as a pseudo laptop and you really only need 1-2 computers with multiple accounts. The iPad is more portable than, lighter than and longer running than a laptop. And as an portable entertainment device, nothing compares to the iPad.
I'm going overboard on using my iPad to try and do as much of what I used to need a laptop for. For instance, this blog entry is being made on my iPad. I have been using Pages and the on-screen keyboard for almost all of my work documents. The touch screen is great. I don't miss the keyboard or mouse at all. This is where computing is headed. But you still don't need an iPad.
So go ahead and get one.