Back, on the Monday after launch (when my 20gb PS3 was delivered w/ 1.00 FW) I made a backup of the HDD (using our friend, dd), before poweron.
PS3 is at 1.31 currently, I figured that I will restore the backup. Took about 30 minutes, and the backup was restored, and the PS3 booted, however:
Users. Profiles, Settings, and more importantly, the Firmware version, all stayed, everything else (otheros install etc) all went the way of the 64DD, they vanished.
So, we can safely assume that Users, their profiles, all the settings, and the firmware, are stored in the Flash(es) on the PS3. Kinda already figured that, however it is good to test!
And, more supprisingly, one can remove the PS3HDD (as long as the otheros is set to boot) and it will boot up the bootloader without a problem, so our beloved hypervisior is inside the PS3 as well (again assumed, but confirmed).
What we do know however, since (which was known for quite a while) if we remove the PS3HDD, the XMB refuses to start up, that critical system files are on the HDD.
The next test (once one can be obtained) is to check if the PS3's HDD's are tied per PS3 (aka use one in another), or if every one works in every console!
I will admit, these are somewhat obvious findings, however they are necessary, as we need to know exactically how the PS3 ticks!