Isn't 8GB a bit excessive, though?
It truly depends on what you do...and the price. If you have the $$ and its $200 why not max out your mobo and never think about having enough RAM. I use VMWare for running virtual machines and its nice to be able to setup a virtual network, domain controllers and clients or just do testing. The 8GB allows for multiple machines running simultaneously.
If your machine is used exclusively for web browsing, movie watching, and gaming then 4GB may be enough. I think 8GB is cheap enough now that there's no real reason not to seriously consider it.