I have wanted a tablet computer like this for many years, and the iPad has exceeded my expectations. My only regret is that I didn't buy 2 and eBay the other at a huge profit :)
Still waiting on my 3G, but I've been using the wifi version for over a month. I really like the touch interface and screen size. My main complaint is that the thing is kinda hard to hold on to. I find myself trying not to touch the glass too much when I carry it around, but because of the sloping back, I've had several really close calls, coming dangerously close to dropping it. Propping it up on a pillow on your stomach seems to be a pretty good way of using it.
I think that a case....just about any case...is essential when carrying the iPad. I agree that losing your grip on it is entirely too likely.
My most current observation is that I now find the iPad difficult to hold without the case. It feels heavier without the case, presumably because I have to grip it harder. I am not a big fan of the rounded back, much prefer flat.
They make cling on skins that would make it easier to hold and protect the aluminum for those who do not want to defeat the size advantage.