I was playing around with one at the Apple Store yesterday. The spacing of the keys is a REAL problem for me. Typing on it feels very awkward.
My MBPs' layout is much better IMO, but THAT keyboard has other problems. In particular it just feels very flimsy. And it just seems like if I use it an awful lot, the paint's gonna wear off the keys.
I've since gotten an iSkin, which I guess helps the feel of the keys somehwat. Even so, I plug in a USB keybaord and mouse when I'm at home or work. The Apple USB keyboard is AWESOME, in my opinion. As is the Mighty Mouse.