For those of you wanting more than 4GB of RAM with Mac OS X, and wanting to buy one of the new 13.3″ Apple MacBooks (or one of the 15″ MacBook Pros that came out last month, you might just be in luck.
Apple will tell you that the maximum amount of memory is 4GB of the 1066MHz DDR3 (aka PC3-8500) RAM. Mac Rumors is reporting that 8GB of RAM causes stability problems with OS X on MacBook Pros , however 6GBs works just fine (8GB is supported by the NVIDIA chipset).
If you are willing to pay $675 (one 4GB DIMM and one 2GB DIMM) RAMJET Inc. will set you up with the proper non-stacked DIMMs (which run cooler and require less power than normal stacked DIMMs).
This is tested on Model 4,1. You can find the memory and more information at:
http://www.ramjet.com/mbib.asp.
Read: ZDNet.com via Mac Rumors