I've not tried the nook, but, of the Kindle and Sony, I definitely prefer the Sony. That's the one I own. I have three friends that have also purchased a Sony after playing with mine, too, and that's after they each checked out a Kindle from our university library for a few days.

In my opinion, the Sony Reader's build quality and general heft (metal casing) is much nicer than the Kindle. The buttons are also laid out much more nicely (you heard right about the Kindle being annoying in that respect). Other things the Sony has going for it are open formats (PDF, ePUB, etc) and far and away the best general management software with Calibre (library organization and book format converter).

Anyway, I can't comment on the Nook, but I'd strongly recommend the Sony over the Kindle, if there's not some important reason that you're leaving it out.

As to your specific question about the internet, yes, that's a huge gimmick at the moment. The refresh rate on e-ink screens is simply too slow. You MIGHT be able to get away with reading some RAFO posts, but general browsing is just too frustrating, as you can't do anything smooth, like, for example, scrolling. Any action you try to do takes between 0.5 and 1.5 seconds to actually show up on the screen, depending on how much of the screen you want to refresh. It's just not a good option at this point.