I've been going back and forth about getting a tablet since the iPad came out a few years ago... the more I think about it the more I start to see a "need" for one, but honestly I keep thinking that I'm just manufacturing a desire to have one.
For my current needs, I have two things I can do: full-fledged laptop (13" MBP) and mobile internet (iPhone 3GS). I can and often do write full-length emails via my phone... it gets the job done when on the road and even with my relatively small data plan (500MB) I can stay connected on Twitter, Facebook, and any other sites I want. The screen isn't optimal but with the new Reader function in Safari (iOS 5) a lot of the pain disappears. It's still hit-or-miss though with functionality at this point.
When I want to do some serious computing or just want more screen real estate and a real keyboard for emails, I grab my MBP. I find I still don't like the on-screen keyboard of the iPhone even after almost 3 years, but at least you can thumb-type with it. To me, the iPad keyboard lacks the tactile response I need for using multiple fingers to type (I can't live without the bumps on the F and J keys).
I also have the issue of the cost of another
cellular data device that performs essentially the same function as my iPhone, except without the ability to send proper SMS and make proper phone calls. I can't keep an iPad in my pocket whereas my phone I can, and if I did have an iPad, I'd likely keep it in a bag the same size as something I could carry my laptop in thereby negating any of the convenience.
Sure, the iPad weighs less than my laptop and the new iPad screen is gorgeous, but if I want to do anything "serious" online or otherwise, I just can't see myself grabbing the iPad over the MBP. If I was looking for something ultraportable I'd still choose the MBA over the iPad because it's still a proper computer.
I'd like an iPad (no other tablets interest me at all) for the sheer gadget-factor, especially if I lived in an Apple "ecosystem" with Apple TV, Airports, and all the Airplay stuff where I could push content to my other devices, but for this moment in time, I'm not in any hurry to drink any more koolaid or part with any more cash