Ars Technica has a review of the Matrox DualHead2Go product. Here's a brief run down of the product:
This device connects two monitors to a single analog VGA out, and uses the EDID standard to simulate the presence of a single, double-wide monitor running at either 2048x768 or 2560x1024, with the desktop spanning over both monitors. In the case of a laptop, the desktop may span over all three monitors.
It sounds pretty cool. I would love to hook one up to my laptop and run with three screens. I currently run dual screens at work, with my laptop as one screen and a monitor as the other, and I love it. I currently only run one monitor at home, but my 6600GT graphics card can support dual monitors. I really need to get that going at some point soon.