I just did this for two systems yesterday;
One old AM2+ Phenom 9000 buld to a new Z77 i5 2500k system and it wouldn't even boot. I made a quick win installation on a spare 60GB had him move most of the important files to a 2TB then had to wipe and re install.
The other system (in sig) I moved from the sig mobo to a Asrock z77 E4 and it boots and 99% of everything seems to work perfectly........that 1% though is kinda huge.....Steam fails to connect online and says my date/time is wrong. Silverlight also refuses to work and I can't use anything that requires it like Netflix
. I tried reinstalling and what not but they both refuse to work.
I have moved a few other systems before and have never had issues with the exceptions of minor annoyances that were eventually fixed with proper drivers and cleaning. Anyways looks like I'll be using Mr Webster's guide again for my SSD later today, But yeah goes to show some issues happens sometimes but other times your fine.