For those of you out there who cannot stand the new cartoony look of OS X 10.10 Yosemite, don't worry, help is at hand.
You will to have a backup of a Mavericks system somewhere at hand to do this though.
Just download and double-click this script to do the magic.
If you get a priviledges error when trying to run the script on your computer,
right-click the script file and select "open" to run it.
Note the script does not do any backups, but it does ask you to confirm each action it does.
You will not be able to undo (easily) any changes it performs.
When you've done all that, you may want to play a nice game of Solitaire on your Mac :-)
The best place for comments etc. on the script is here.