You know the odd thing about this thread is that we seem to be arguing about WPM and the like, as though we were all a bunch of secretaries (not that there's anything wrong with secretaries) intent upon using this device for routine clerical work.
There's a difference between writing and typing, after all. I've found the iPad to be a very pleasurable tool for writing -- I use it by choice for most of my work now. No doubt my raw character-input speed is lower (I haven't tried to measure it), but in my experience, this isn't the limiting factor in how quickly I'm able to produce finished written documents.
I think the OP's comments about editing are well taken. iPhone OS's way of handling these tasks takes some getting used to, to put it gently. The whole select-and-cut-and-paste procedure is a lot more cumbersome than dragging text around on the screen with a mouse. But in some ways I don't think this is such a bad thing -- it pushes me a little harder to compose my thoughts more carefully on the first take.
As to the iPad's onscreen keyboard, I actually think it's pretty cool, now that I've gotten used to it and figured out the shortcuts and so forth. (I find it moderately irksome, for example, that the computer keyboard I'm using right now actually requires me to TYPE such things as periods, apostrophes in words like "don't," and the final letters of words like "keyboard" when it ought to be perfectly obvious where I'm going.) I bought both a bluetooth keyboard and the keyboard dock along with my iPad -- I write for a living, so I wanted to make sure I had the best tools for the job -- but in practice I no longer use either of them.
And just to reiterate: this has nothing to with raw typing speed. This is strictly an intuitive, personal, maybe partly aesthetic, "look and feel" kind of thing. I enjoy the iPad keyboard and I am actually getting real work done on it.
But really we're comparing two rather unlike things, I think. Some people prefer taking notes with a pen on paper to typing them on a keyboard. Speed isn't the issue -- it's something less easy to pin down. One of my favorite novelists, Vladimir Nabokov, composed his fiction by hand on index cards. I have no idea why, but strongly suspect it wasn't because he was an extremely fast scribbler with tiny fingers.
So maybe I'm suffering from fanboy syndrome or some other deep character flaw. But I hope this flaw will help me finish my novel-in-progress. It was due over a year ago.