"I have the 3g version and I have free instant access to the internet from anywhere in the world".
Yes, friend of mine was on a tour of the Panama Canal, so while there he bought a book about it via 3G. Mind you, if he'd waited a couple of hours he could have used the free wifi on his cruise ship.
Personally, I doubt I'd ever use it, because (a) a wifi connection is never far away, and (b) I find it much easier to browse and purchase from Amazon on a PC.
The only time I wished I had 3G was when I was on the beach, got to the end of a book, and was offered the chance to buy the next in the series. But even then, a 50 metre stroll put me in range of the free wifi of one of the beach bars.