With multiple computers in my house, it's always been a desire for me to be able to stop what I'm doing, go to another computer, and continue on. I've been doing that by saving and reloading on another computer, or I'll remote desktop in to continue. But with USB flash memory sticks getting bigger and bigger, it's now possible to carry my computer setup with me to any other computer in my home!
By using a 16 or 32 GB USB memory stick (actually, any large portable memory device would work like a hard drive, iPod, SD Memory card, etc. The faster the better), I can create a virtual machine system on that flash memory stick! On each of the host computer, install VMWare's free Server virtual machine software (on the Mac, install Fusion). Create a virtual computer and save the files onto the memory stick. Once the system is configured the way you want, you now have a virtual machine you can start up and continue to work on from any other computer in the house! Instead of shutting down the virtual computer, just pause it in the VM to put it to sleep. It'll save your last state onto the flash memory stick so that when you start it up again on another computer, it'll start where you left off.
Because flash memory is much slower than regular memory or even hard drives, and because your memory stick probably doesn't have that much more space after the OS and your applications, you should create a shared folder on a fixed system and in the virtual machine, map a drive to that shared folder. Now you can save any and all data from your applications on the shared drive instead of the flash drive! If you need to take the data/file with you, just drag a copy onto the virtual machine's desktop.
Ingenious and free (except the memory stick)!
The biggest limitation of this setup right now is you can't play 3D games or games that require hardware acceleration. Hopefully VMWare will create a virtual DirectX layer like they're doing with the Mac version in Fusion. When that is fully compatible, even taking games with you from one computer to another will be possible.
I also recommend you stock up on memory for each of your host computer. Memory is cheap, and the more you have the better, even if you don't plan to use them as virtual machine hosts.