As I've been playing around with the Kindle 2, I've discovered a few interesting things that I haven't yet found documented elsewhere. (That's not to say they're not documented elsewhere, just that I haven't found them).
Table support - The K2 supports basic HTML Tables in mobipocket ebooks. I haven't done extensive testing. But, unlike the Kindle 1, the support is there.
Proxies - Amazon proxies all web traffic for your Kindle and restricts which ports on remote servers you can connect to.
USB Networking - http://igorsk.blogspot.com/ is the place to go to learn about Kindle reverse engineering. One of the things that Igor mentions is the "extra" shortcuts baked into the Kindle.
One of the commands Igor mentions is ";debugOn" - This turns on the Kindle's extra commands. This works the same on the K2. Once you've done that '`help' will show you a list of private commands. There are a couple private commands which appear to be new for the K2: '`usbNetwork' and '`usbQa'. Being the sort of guy I am, my eyes lit up when I saw these commands. So I plugged my K2 into my trusty Macbook Air and ran them. ...and got nothing.
As you can see from my previous post, I've been a bit busy on other K2 related hackery. I moved on and mentally filed the `qa command away for later.
The next day, I plugged the K2 into the MacBook to download a test book. The Kindle didn't go into disk mode. Just as I started to wonder what had gone wrong, the MacBook popped up a dialog telling me that a new USB Ethernet device had been detected and would I like to configure it now.
A few minutes with tcpdump later, I'd set up the MacBook as 192.168.15.200 and could ping the Kindle on 192.168.15.244. No, the Kindle is not listening on any ports out of the box.
Since I know a few of you are asking, no, the Kindle is not acting as a gateway to the outside world. You can't (and shouldn't) use it as a 3G modem for your laptop. Amazon is almost certainly paying by the byte for your traffic. If you figure out how to start abusing the Kindle's network, 1) it will be very easy for Amazon to catch you and 2) Amazon knows who you are and where you live. (and where you are right now thanks to the Kindle's GPS)
It's pretty clear to me that this USB networking mode is primarily intended for testing, debugging and development. I look forward to seeing some interesting testing, debugging and development.