Here is my experience using sysprep to do a mobo/cpu swap. I am 1 for 2.
First scenario was with my older Windows 7 pc, so lots of data and apps on it. It has a retail OEM license. Went from an Intel setup to an AMD without a hitch. Windows even re-activated all by itself. Yay!
Second scenario was going from an AMD CPU/VGA to a new AMD APU. This PC has an UPGRADE license. After getting around the "can't do sysprep on an upgrade version", I thought I'd be cruising to success. No such luck. Windows refused to start, and was even unable to repair itself. Luckily there weren't any important files, so I just did a fresh install. I'm sure I'll have to call to activate, as I've already used the key for a fourth time. Have no clue what went so wrong here, but I'm suspecting the major change to an APU. It's interesting to note that vga was still low-res after the re-install, which it's never been with any other of my many setups. Either that, or sysprep on an Upgrade install doesn't clean up as well as the other versions.
EDIT: I just realized that the new motherboard came with UEFI BIOS, not sure if it was enabled in that mode but I assume so. Maybe that's what caused the major snafu?
Just my story, for those of you scoring at home.