[AltecXP]

I know the official numbers are 4 but has anyone tried more? If it doesn't work is it a hardware or software limitation ?

[Simon]

From the MacBook RAM upgrade sticky thread

Originally Posted by Simon 

Both the unibody MB and MBP are specified by Apple to support up to 4 GB of RAM. The MB and MBP however have already been shown to accept, recognize, and use 6 GB of RAM (one 2 GB and one 4 GB SO-DIMM). It will boot and run with 8 GB (two 4 GB SO-DIMMs) too, but as of right now, it is not stable. It has been rumored that a future firmware update could change this.

[ghporter]

AltecXP, I hope Simon's response-and the link he provided to the sticky thread that has covered this subject VERY thoroughly-answers your question. The SIX GB RAM limitation seems to be all firmware-the logic board can't handle 8 because of the firmware.