I have a late 2008 macbook unibody and put 2 x 4gb 1333MHz ram in and it worked, but I do get occasional program crashes, especially for games. With 4GB 1066 ram it is fine.
There is a different firmware EFI update for the unibody macbook that allows it to work ok with 8GB ram, earlier updates will only support 6GB, any more causes constant system crashes. You do need a late version of Leopard at the very least to make it work as well. I think all 10.6 (Snow Leopard) variants work OK. To make things more awkward, Apple released the updated EFI with the same version number as the old one. You need version MB51.007D.B03 (look under boot ROM in system profiler). If you want more info look here: http://blog.macsales.com/9102-secret-firmware-lets-late-08-macbooks-use-8gb
In summary, use the 1066 RAM if you want a totally stable machine. In most cases it will actually be faster because it runs at the bus speed.
Chris