I used to run 2 x GTX 275 in SLI and I never noticed micro-stuttering. I'm not saying it never happened, I'm just saying I never noticed it. I never had issues with games making use of both video cards in SLI either. Timely driver updates from nvidia pretty much guaranteed a good experience with SLI in the newest games. My only complaint with SLI is that it generated a lot of heat, crowded the inside of my case and it draws a lot of power. I upgraded to a GTX 580 about 10 months ago and it outperformed the 2 x GTX 275, produced less heat and drew about 100W less power.
"Looking for brahs to come fight crime with me" - Unload
No micro-stuttering here and I have two GTX460's. I have a 120hz 3d monitor though and try to run games at a high fps even if I have to turn down some settings. So if I'm getting it I won't notice it as much.