The Nvidia gpus/drivers suffer from microstuttering too.
Not to mention other issues.
For example, it is rather difficult to get two Nvidia cards obtained from different vendors, which deviate from the reference specification, to cooperate in SLI. From a pool of six different GeForce GTX 580 cards, only two would work together consistently. From a pool of five different GeForce GTX 570s, only three would. We had problems mixing clock rates, BIOSes, supporting platforms, and so on.
However, we all know that 1 video card is better than 2 in many different way which is why I would never build a Xfire/SLI setup.
I've owned the 4XXX, and 5XXX cards over the last 3yrs and I only had trouble with one driver, that was 11.7 which made my idle clocks too high which made my gpu run 55c on idle.
At least it didnt cause my card to overheat and fail like some recent Nvidia drivers I know of. lol