I have the Packard Bell version (nearly identical specs to the Aspire One but with a 120GB HDD).
Based on the videos I found on Youtube and my experience working on mine, I'd say that the hardware is actually the same, but the shell is different.
The 8GB SSD should be the same size as any regular 2.5" HDD, so it should be easy to upgrade to any HDD up to 500 GB (some 1TB ones may fit, but most are too high to fit the HDD cradle).
There's also 2 SD card slots, one of which is claimed to seamlessly integrate with the SSD. So with a 32GB SD card, you can have 40GB of storage. I haven't verified this claimed integration myself, but read it while looking for the exact specs of the SSD version.
Like was8v, I upgraded mine from 1GB RAM to 1.5GB. The upgrade required a nearly complete tear-down, but was easy enough with the help from this video
I also swapped my original 120GB HDD for a 250GB WD caviar black while I was at it.
I can verify that a full XP will run with the stock 1GB of RAM, but it stands to reason that "Tiny XP" or Linux will be faster.
I'm running fully loaded and updated XP, Vista, Win7 and Ubuntu 10.04 in quad-boot configuration on mine, and can't really complain about the speed in any of those operating systems.
Unfortunately mine is starting to have problems with the right-click button, so I'll need to look around for a replacement soon.
Shame really, as I recently purchased a 10.200 MAh battery (which boosted working time from around 3h to 12h+) and was planning to replace the HDD with a 240GB SSD.