Never mind... I think I answered my own question.
The Apple Store (UK) says:
"The MacBook uses one of the fastest memory technologies available today—667 MHz, double data rate (DDR2), synchronous dynamic random-access memory (SDRAM). It ensures high performance and reliability by synchronizing memory speed with the speed of the central processor so that data can be delivered continuously and more rapidly to the processor. And if both slots are loaded with an equal amount of RAM - which is strongly recommended - you can take advantage of the system's dual-channel memory architecture for an additional performance boost. With a dual-channel memory interface, both banks of SDRAM can be addressed at the same time, enabling MacBook to reach a memory throughput of up to 10.7 GBps."
(Sorry, can't link to it - timed session, and I don't have anywhere to host a pic).
Looks like I'll just BTO with 1GB. Happy days!
