During the holiday shopping season, I couldn't resist the RAM deal of getting one 2*4G DDR3 set for 90 bucks. then replace the original 2*2G set and power on, the Mac just works without any problem for a week now.
so the spec on apple.com is incorrect, it says it could support Max 4G ram. here is the spec in http://www.apple.com/macbook/specs.html
“2GB (two 1GB SO-DIMMs) of 1066MHz DDR3 SDRAM; two SO-DIMM slots support up to 4GB”
My hardware spec, the late-2008 version. And I wrote a simple java to reserve more RAM over 4G, it works
Model Name: MacBook