this is the result of my first day off work :-) I spent it hacking on my PC, and you are welcome to profit from it.
It's a VNC viewer for the Kindle. It still has it's restrictions, and it does not yet handle input. You can however use it as a e-ink screen for you PC. In order to do that, you need to run a VNC server on the PC.
E.g., on Linux, I run
xinit /usr/bin/openbox -- /usr/bin/Xvnc :1 -geometry 1200x824 -depth 16 -dpi 160 -alwaysshared -lazytight
to start up the VNC server running an instance of the OpenBox Window Manager.
Then I call
x2vnc -east localhost:1
to use my mouse and keyboard from my "main" X server, simulating a screen transition on the right ("east") side of my main X display. (Note that for me, the x2vnc app is a bit broken right now, but it works well enough.)
On Windows, you would probably use some virtual second screen and use a VNC server that provides the contents of this screen or just fire up a VNC server and work on a clone of your main PC screen.
The attached ZIP archive contains runnable executables and a file INSTALL.TXT which explains how to install the application. It also comes with a config file for Launchpad.
It's tested on a Kindle DX Graphite and a Kindle 3 Wifi at the moment, also a test was done for the K4. Your connection options would be USB or Wifi (on K3/K4/K5).
The source code is available at http://github.com/hwhw/kindlevncviewer
Update 2011 Oct 04
: Added support for password-based authentification. See the included launchpad configuration file for an example. In short, it has 2 new optional arguments now: "-password <pwd>" which will read a password given as the following option, and "-readpassword" which will read the password from standard input, so you can pipe it from a command or a file.
Update 2012 Mar 05
: Added input support. This works by doing a callback into a Lua file. Currently, keys are passed to host mostly as-is. Page Forward is mapped to TAB, Page Backward is ESC. When you press Home, the viewer will quit. But you can edit config.lua and have you own layout or even macros by just scripting them in Lua. Also, I've prepared a callback function for pointer movements. Maybe I'll script that soon or someone beats me to it.
Update 2012 Apr 17
: Added dithered mode. This isn't very usable, but it will not flash the screen at all (i.e. not going through black). It only paints white and black pixels to archieve that. The backside is that only high contrast parts are visible. It is more or less a play thing. You can activate this mode by giving the "-dithered" switch on command line. Except for this new play mode, update doesn't bring any new stuff.
Update 2012 Oct 05
: Added support for 8bpp framebuffers (should now work on K2, KDX, K3, K4/K5, possibly KPW. No dithering support for 8bpp for now, that was a proof of concept anyway. The call to kaffeine was factored out (it now uses the LIPC mechanism) and a host shell script for creating an Xvnc server plus calling kindlevncviewer via ssh was introduced - thanks to dpavlin!
Update 2012 Oct 27
: Added missing files, otherwised unchanged to Oct 05 version.