My MacBook shipped with the standard 2GB of memory. I had the idea of adding the additional 2GB myself since Apple charges you more money than needed. Downside is that the new MacBooks are kinda sensitive about the memory you use. Regular Kingston / Sandisk memory could result in kernel panics (or other strange behaviour).
After some googling I read some forum posts on OCZ memory and the new aluminium MacBooks. Today I added 2 * 2GB of OCZ memory to my MacBook, and it runs fine (at the moment).
As long as there aren't any updates on this post it probably means that I'm not having any problems with the new memory.
Memory details:
OCZ SO-Dimm 4GB (2x2GB) DDR3 PC3-8500, 1066Mhz