Pretty easy! However, watch that sleep sensor/ribbon cable. Pretty easy to damage that during the fiddling process of removing it. Also, the adhesive on the replacement cable may still have on it seems to arrive melted via the shipping process. So make sure it hasn't gotten on anything else. Initial symptoms of the HDD cable failure were: slow indexing speeds, spotlight wasn't working, displaying directory listings were slow, complete OSX panics, OSX freezing, HDD folder appearing with question mark on boot. Disk Utility would randomly see the HDD but anything mounted externally it had no problem.