I am in need of some educated opinions on the differences between several video cards. GTX 560ti 1GB or GTX 560ti 2GB? What are the performance gains from having more memory? Am I likely to notice when playing the average game, or using graphical intensive apps? How about the jump to the 580? Is spending an extra ~200-300 dollars worth the performance difference? I am in somewhat of a quandary because I sort of need (well, okay - "want") a top tier card, but buying at the end of the cycle, but too soon for the next cycle (Kepler) causes some anxiety. Spend $5-600 on a GTX 580 and keep it for ~2 years, or $200-300 on a 560ti, and replace it in ~6-8 months when the next gen. cards have been through a proper shakedown and have proven reliable?
VRAM becomes necessary at high resolutions. If you're playing at 1920x1080 or lower, don't worry about it.
I think the new cards are going to crush the 580's value, so you're better off going Ti for now, or even with a 6870. That card'll run just about everything at medium-high settings (assuming 60fps). $145, versus the Ti's $220ish: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
If you are going to spend $500-600 buy a radeon 7970.
If you are gaming at higher than 1920x1080 then more than 1gb of vram is suggested. Some people even report maxing out their 1gb vram (with ultra-res texture packs) even at 1920x1080. Generally speaking though, 1gb is enough vram for 1920x1080 and lower.
I haven't looked at specific prices but a gtx570 will do 1920x1080 really, really well. A 560ti is enough for that resolution, but a 570 just does it better and is much more affordable than a 580. All of these cards SLI/Xfire very well for future upgrading if your rig can do it.
Waiting for Kepler depends on how badly you need to upgrade now. I wouldn't buy a 580 - since the 7970 is out and comparably priced. A 560ti, 570 or 6870, 6950, 6970 are all very nice and are magically priced close to their performance ranks. Personally, if I could afford it, I'd buy a 7970, but I game at higher than 1920x1080 - your situation may be different.