From Anandtech.com:
"The MacBook Pro features Intel's 945 Express chipset, but opts for a faster external graphics solution rather than rely on Intel's integrated graphics. Being based on the 945 of course means that it features a dual channel DDR2-667 memory controller, but in order to take advantage of that you have to populate both SO-DIMM slots on the MacBook Pro. There is no performance benefit however to enabling dual channel mode; remember that the Core Duo only features a 64-bit wide 667MHz FSB, and without integrated graphics a single 64-bit DDR2-667 channel can offer enough bandwidth to saturate that bus. If the future MacBooks (non-pro) do ship with integrated graphics, you may want to install memory in pairs as dual channel will matter there.
To confirm that dual channel does nothing I ran a couple of tests with a single 1GB DDR2-667 SO-DIMM vs. 2 x 512MB DDR2-667 SO-DIMMs:..."
http://www.anandtech.com/mac/showdoc.aspx?i=2740&p=4
The new C2D MBPs still uses the 945 chipset so it doesn't change that fact.