I'm not going to panic just yet. I have two GTX580's in my machine. But the ONLY reason why I have that is to add some extra beef to my games when I run on my monitor's native resolution of 2560x1440. Having two GTX580's for a monitor with a max resolution of 1920x1080 is overkill - but see what it does when you bump up the resolution. That's why I had to get a second card.
I'm really hoping to run this game on high-ultra settings without issues, but it's becoming more and more of a question mark at this stage. We also need to keep in mind that it will be about 2 - 3 months after BF3 is released for all the graphics card manufacturers to release some proper drivers for the game as well. So even if your performance is slow at the very beginning, you could probably look forward to a 15% - 20% increase in performance as time goes on with new driver releases and game patches being released.
At the very least, DICE owe it to the community to deliver a game that at least looks as good as BFBC2 - even in medium detail. If your current PC can't handle BFBC2 on high settings now, then you don't really have grounds for complaining when you can't run medium settings on BF3.
That being said, I look forward to seeing that BF3 does to my machine. I've spent quite a lot of money on my current setup to enjoy this sort of game to it's maximum potential. I just hope that the strain it puts on any of our PCs is due to a very high quality graphics engine, and not due to sloppy programming as was the case with Crysis 1 and GTA: IV.