I run SLI 570s 1.28gb and I can vouch for running out of vram, however, it's not as bad as people make it out to be. Here is my experience, and here are my specs and game settings for reference.
i5 2500k @ 4.5ghz
SLI GTX 570s @ 800mhz @ 1080p
4x MSAA, Low FXAA (I hate the blur)
Large 64-player conquest maps
I normally run at 80fps on average, drops to 60s when over viewing the entire map, 100s when hiding behind rocks/bushes. Looking at my GPU vram usage, it's always around 1100, so pretty much maxed out, but I still get very smooth, playable performance. If I sat down for an hour to play, my game would stutter, maybe 5 times in that 1 hour. Many people would find that unacceptable, but I've come to terms with it. It only occurs when something really intense and crazy happens, ie. jets crashing, 2 tanks shooting me at the same time and 4 players on screen, so it's understandable for my vram to hit a big wall because of what's going on on-screen. My fps drops from 80 down to 30 and gets unplayable because it's all jerky and gets stuck at 30 or so fps for about a second until I look away. 5 times in 1 hour is not bad at all.
Turning down MSAA to 2x smooths it out a lot, and can hardly notice a graphical difference unless you pixel peek. MSAA is what chops the fps and vram down. If I got 80 fps on 4xAA, I would get 95 on 2xAA and reduce those vram walls from 5 down to 2-3 times an hour.
This is only in effect for large 64 player conquest maps. In 32 player or smaller team deathmatch maps, single player campaign, I leave 4xMSAA on, and I get 0 micro stutter vram walls. I can play for hours without a problem with only 1.28gb of vram. Even though BF3 eats vram and running the 570s at max, it's coded and utilizes it very well to ensure me a smooth performance, 95% of the time. I contemplated on getting 2gb 6970s CFX, but I'm sure that the Radeons will have problems too, granted it might be a little smooth when ***** starts to fly, but I know when you have 2 jets crashing, 2 tanks shooting at each other, 3 people trying to blow up tanks, all on your screen, I doubt the 6970s will handle it at buttery smooth fps at 4xMSAA too.
Depending on how future games utilize vram, I know my 1.28gbs aren't going to last me too long, and the 2gb vram will become standard very soon, but 1.28gb is fine for now. Of course, at 1920x1080, maybe 1920x1200 ONLY. Anything higher, then 1.28gb is totally not enough.