Ah, now here we see the problems that habitat87 is causing...
To be fair to hab, there's a pretty good chance that more than 4GB of RAM IS a bit of a waste, at least in the sense that you may not notice very much of a difference in what you're running TODAY between, say, 4GB and 6GB.
But if you're buying an i7 system, that means 3-channel memory. So you basically have a choice between 3GB, 6GB, or (and this probably IS a waste) 12GB.
IMHO with RAM prices as cheap as they are today, it would be short-sighted to buy 3GB and install a 32-bit OS. Software abhors unused memory, and over time with new releases it grows to fill whatever RAM is available. Although you may not see much of a difference with the software you have NOW, I have no doubt that next year or the following year's games WILL be taking advantage of that memory. They'll do it because RAM will be cheap enough that every new system will come with 4GB at a minimum, and because the video game industry is competitive and will look for ways to use whatever hardware they can to make their games better.
So go ahead and buy 6GB and use a 64-bit operating system. You may not NEED it today, but if you keep your system for a year or two you WILL need it eventually. And it's so much easier to install the 64-bit OS now than to start with 32-bit and then have to reinstall and rebuild everything later on.