I put Windows 8 on the Mini 9 during the early beta of it - haven't really used it much at all. I hate the "interface formerly known as Metro" when using a non-touchscreen device, and have decided to not upgrade to Windows 8 on my regular PC. On the Mini 9, Metro apps won't run because of the 600 pixel screen height. On larger models with at least 768 pixels that isn't a problem.
As for replacing the RAM, on some models it is easy, on some you do indeed have to disassemble the whole thing, and on others (such as the 1010) it requires replacing a daughterboard that also contains the CPU.