Here's the relevant header info:
HTTP_USER_AGENT: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 4.0) NetFront/3.3
HTTP_X_FORWARDED_FOR: 22.214.171.124, 10.0.52.11
HTTP_VIA: 1.1 (amazon proxy)
HTTP_ACCEPT: image/png, image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, */*
Because the internal browser is already doing paging, I used the above info to make sure that I deliver full pages through the Mowser content adapter - as it was confusing otherwise - and it seems to work pretty well. If you get a Kindle and want to use the browser for any realistic amount of time, I'd definitely recommend using Mowser, as the formatting ended up being much more readable (if I do say so myself), and you end up with less paging because of the more compact markup, and reduced image loading. Here's a high-resolution example of the New York Times on the Kindle via Mowser.
All-in-all it's a slick little device. The navigation for the web is a bit wonky - there might be a way of making more "Kindle-specific" GUI features which will help, but in general if you were to choose a reader, the free mobile browsing itself is worth quite a bit. We'll see how long *that* lasts, actually... I bet Amazon will be surprised at how much people circumvent the $2 per feed per month (!!!) charges and go directly to the sites themselves using proxies like Mowser. Someone's going to have to foot the EV-DO bill, and profit on the books only goes so far.
If you have any other mobile-browser specific questions, email me or leave them in the comments, otherwise check out Diego's second take on the device for more info on the device overall as well.
* The ABC123 stuff above is in place of some identifier info that Diego would rather I leave out, for understandable reasons. :-)