in your MacBook
"To Pair or Not to Pair"
Since day one, Apple has strongly recommended that memory going into models with the Intel GMA950 Video chipset be installed in pairs. GMA950 video equipped Macs do not have dedicated Video Memory for display and rather the GMA950 actually shares 64MB from your main system memory installed.
As all of the Intel Core 2 Duo Macs (same is true between Core Duo Macs) share the same memory controller and processor. It is only on the GMA950 equipped models, which have the shared memory use for video, that are pushed to have only matched pairs of memory installed - for enabling the 128MBit memory addressing. In the Apple store, you'll find that while the current Core 2 Duo models with Nvidia or ATI video offer memory options on non-pairs - the GMA950 equipped model configs offer memory options that only include pairs.
Despite Apple's strongest recommendations for memory pairing, the test results we have from the current Apple MacBook 1.83GHz 13.3" Core 2 Duo laptop cause us to recommend otherwise. When the iMac G5 came out, paired memory for performance interleaving was an option there as well - but testing showed that you were better off upgrading to have more memory via replacing one module than buying less memory so the budget could support two modules. We really believed that it would be different with these GMA950 video equipped Intel Macs because of them sharing the system memory - something that wasn't a factor with the iMac G5. The bottom line is that it's not at all what we expected.
Apple MacBook Memory Testing of 512MB, 768MB,1.0GB, 1.25GB, 1.5GB, 2.0GB and 3.0GB configurations by Other World Computing.