Quote: "considering NO single 3d application currently released ON EARTH (save 3d modelling programs like autoCAD) uses more than 512MB of Vram"
Eh? As I said, GTA4 uses something like 1400mb at max graphics with 1280x1024 resolution. Here's a couple links with some memory usage of some games:
http://www.yougamers.com/articles/13801_video_ram_-_how_much_do_you_really_need-page7/
http://forums.anandtech.com/archive/index.php/t-34748.html
So really, 512mb-1gb should be enough. Keep in mind modern games will continue to use more memory as they will continue to use higher resolution textures. I'd say, for a card that you'll have fun with for the next 1-2 years (at least), go for a 1gb vram card at a minimum.
I do want to say, from personal experience, vram makes a huge difference, when you don't have enough. Having too much is a waste, but not having enough is detrimental to fps. For example, I had a 8800gt when I got tomb raider underworld. That card could easily, and I mean, easily dominate that game, but since I had only 256mb of vram, I could only run with low to medium textures, otherwise it would easily kill the frame rate. It'd go from a cool 100+fps to 20-30.