My 2G iphone and 3GS have been running very well since we got them. Now my mom is using the 2G one.
I find that for an all purpose device, it already works very well. And really, if the iPad can only use an iPhone-esque OS, it's too crippled to be worth another 500 bucks.
If this only ran OS X, I would really want it. Bad.
Perhaps for people who don't already have an iPod touch or and iPhone, the iPad would be a pretty good deal though.