Via a link on XLR8yourMAC.COM I found this article about pairing memory in your Mac to increase performance.
Being on a budget myself ... I was having a hard time justifying two "exact same" 1 GIGABYTE SODIMMs (laptop memory) for my MacBook. After consulting with a friend that I consider an expert in such knowledge ... he made the case that "more memory is always better" than "less paired memory". So ... when I downgraded a recent MacBook that came in for repair and ended up buying ... I decided to put the 1GB DDR2 from it and add it to my 512MB (replacing one of the 512MB SODIMMs).
After reading the short but sweet and backed up by benchmark analysis that Other World Computing did - I can see why my friend was right - more memory is almost always better - especially if you have integrated graphics like some Macs do - that share system memory as VRAM.
Take a look - one of the best explanations/recommendations for memory I've read:
To Pair Or Not To Pair