While I'll agree that it makes things snappier(though I pulled 2 and went down to 4gb so I could use the 2gb in another machine) I would say that unless you have felt your system slowing or you plan on doing something really ram intensive, it will likely not be worth the money. If you have spare ram laying about though, throw it in, if you're running Vista your OS will love it.
As for some realistic numbers, on XP Half-Life 2 loaded to the main screen in about 45 seconds, in Vista(same exact machine, both blank installs) after 3 loads it was down to 20 seconds to load. Not bad at all imo considering that Half-Life 2 has one of the nastiest initial loads I have ever seen. Barring Morrowind on the Xbox that is:)
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