Corsair sent us a PDF document before which takes 13 pages to explain why 4GB of memory is better than 2GB. This, of course, coming from a memory company, who is looking to sell as much of the stuff as possible.
Okay okay, we're sorry Corsair. The document actually goes into quite good detail about the differences and some in-depth testing in several games including Company of Heroes, Crysis and Flight Sim X.
If you are interested in a bit of a memory lesson and why you should buy more memory than you already have, click here to open up the PDF and take a look.