We currently have four active OSX devices plus a couple of first edition Mac Book Airs that have seen better days.
Probably the only Mac fix I have worth sharing is my power supply fix. If you use the new Magsafe 2 (T) power supplies for a while, you will probably notice that the cord frays and splits at the T end. It is a design fault that Apple has done nothing to fix and the only official solution is to pay $85 or so for a new power brick.
There are many suppliers of OEM cords and online instructions for opening up a power brick and installing one. But this is a lot of rather fiddly work and you can only do it once because after you are done you will need to glue the brick back together.
Fortunately there is a much easier and better solution. There are several suppliers of Magsafe 1 and 2 cords that terminate in 5.5 m barrel plugs. The intended use is to plug them into a large lithium ion battery. The cords cost less than $5 on Ebay and soldering a mating barrel connector onto the end of a power brick takes only a few minutes.
[Pics go here]
If the cord ever frays again, just throw it out and use a different one. I keep a stock just in case.
As a bonus, you can now convert your old Magsafe 1 power bricks to Magsafe 2 and vice versa.