Wow. Lots of misinformation here. 2GB is pretty much the standard amount right now. 4GB is becoming more popular as Vista adoption grows, but it's still less common than 2GB.
If you're running Windows XP (32bit), you're limited to a maximum of 3.25GB anyway. Really, the time to switch will be when/if you decide to switch to Vista (or 64 bit XP). Vista is much more memory hungry than XP, so moving to 4GB+ makes a much bigger difference there.
As for how long you can hold out, I'd say you're good for at least a year, maybe two (again, assuming you run 32bit XP). With Vista's lack luster reception, a lot of people are still running 32bit operating systems, and game makers know it. It's going to be a couple years before any significant amount of games really require 4GB of RAM or more. And when that does happen, those games will require Vista (or the upcoming Windows 7), so you'll have a clear sign for when to upgrade.







