simon,
Duane responded to a similiar question at the end of the topic here, http://forum.chumby.com/viewtopic.php?id=1665.
Here is his response...
"There have been three basic versions of the chumby released into the wild, with the codenames Foo, Katamari, and Ironforge.
Foo and Katamari were alpha prototypes, Ironforge is the production unit you have.
There were about 250 Foo chumbys, mostly handed out at Tim O'Reilly's Foo Camp in August of 2006. There was a slight hardware modification (the addition of the accelerometer) for the Katamari chumby - there were about 500 of those built, again handed out to developers and partners. Foos and Katamaris look identical - they have a cloth enclosure, are slightly larger than the production model, and the screen always falls out. They have a 200 MHz ARM9, only one USB port, only 32MB RAM and don't have the microphone. Neither Foo nor Katamaris were ever for sale.
The model you have is an Ironforge, which in in the leather enclosure with two USB ports and the 350MHz processor, 64MB RAM, and has the microphone.
In the Control Panel, select "Settings", then "Chumby Info" - you should see a hardware version of 3.7
Foo is 1, Katamari is 2, Ironforge is 3. We're on the 7th revision of the hardware for Ironforge - the previous 6 versions did not ship to customers, but were development versions in engineering.
There will undoubtedly be more minor revisions of this model - typically part substitutions for cost or availability, and perhaps some board layout changes to increase yield and ease of manufacture. This happens with any such device, so it's possible if you buy another chumby in a few months, it might be slightly different, and have a different hardware version number, say, 3.8. The vast majority of such changes are unlikely to be visible to the casual user - you'd probably have to open up the device and compare the circuit boards and part numbers side-by-side.
At this point in time, there are no new models in the production pipeline, but obviously we reserve the right to evolve the product as needed to address the market - just like every other company that makes products."
-HuckFinn