Adding more RAM than approved. Not recommended.
Some guys say it is no problem - Apple is sneaky and doesn't tell you that you can easily add more: But I got loads of Kernel Panics.
Following some internet threads I added 16GB Corsair 1600 MHz RAM to my late 2011 Macbook.
It worked like lightning and seemed fine at first but I got loads of Kernel Panics.
So I replaced it with 8GB 1333 Mhz Kensington - and am back to a stable system.