Ramjet now offers the ability to upgrade the new aluminum MacBook and the black bezel MacBook Pro to 6GB via one 4GB SO-DIMM module (US$599) and one 2GB module ($75) to reach the system maximum of 6GB.
According to the company the modules are fully compatible with the latest Apple firmware, and are SPD configured for the MacBook and MacBook Pro.
The newest MacBook and MacBook Pro with the black bezel surrounding the monitor, require DDR3-1066 memory (also called PC3-8500).
Ramjet uses a non-stacked module for the 2GB and 4GB module for the MacBook. The cheaper stacked IC variety of 2GB and 4GB SO-DIMM run hotter and draw more power, which hurts performance and decreases battery life.
Although the 4 gigger is a little expensive, if you need the RAM, you need the RAM. The Ramjet 4GB modules are shipping now and come with a lifetime warranty.