DDR2 could probably be called the most popular choice of RAM among current-generation system builders. With Windows Vista becoming the target for gamers wanting to play in DX10, people are increasing their RAM amounts to compensate for all of vistas slowdowns and memory hogging. 4 Gigabytes is being called the sweet spot by many, with 8 Gigs being the future for power users on vista. 2 gigs would be pushing it in vista, as just loading the OS to the desktop will more than likely use half of that, maybe even a third depending on what else you run in the background, meaning you're not leaving much for other applications, let alone todays demanding games.
The GSKILL 4GB DDR2 800 kit installs with ease, as most ram does. I had no stability problems at all in my experience. Overclocking was decent, and it really wasn't limited by my ram, it was limited by my board. This is a pretty good value as far as I can tell. When I bought it, I paid $155 in October '07. At the time of this review, roughly a month and a half later, it can be found for a little over a hundred on some sites. With DDR3 still being ridiculously up there in price and not appearing to be coming down anytime soon, I think this kit is a great investment, leaving room for 2 more sticks for 8GB on mainboards that have 4 DIMM slots.