Johnathon Suker <firstname.lastname@example.org> commented that my technique of copying new System Folder files over the old ones and then moving them all back again could lead to trouble if some old and unnecessary System Update file or something similar was included by this process. I should have mentioned that I always go through the resulting folders and manually scan for files I know won't work with the new System. A slower method might involve opening both the old and the new folders and manually moving (from the old to the new) just non-Apple files that you know will work. [ACE]
Single Time Machine Backups
Tired of Time Machine running all the time? You can turn it off in the Time Machine preference pane, but still initiate a single backup by choosing Back Up Now from Time Machine's menu bar icon. Of course, your backup is much less likely to be up to date, but Time Machine won't be taking any resources while you're trying to work.