I know of sites that sell 8GB sets for the MacBook. Apple states that they can have up to 4GB. One of my co-workers got her first gen MacBook to 6GB. Can anyone confirm that 8GB is recognized in last year's MacBook?
EDIT: My model is MacBook7,1.
Yes, it supports up to 8GB of memory. Make sure that memory is 1066 MHz, not 1333, or you'll be unable to boot to MacOS.
If you are unable to find 1066MHz DIMM, you could be able to re-flash the SPD chip of a 1333MHz DIMMs using a technique I described at the Apple Discussion Board. Note that not all 1333MHz chips can be flashed.
It depends on your particular model, but I believe that the answer is YES! The great people at Other World Computing sell RAM upgrade kits for MacBooks.
To be sure:
If it is MacBook 5,1 or 6,1 or 6,2 you can put 8GB of RAM in it.