I posted this in the official EU forums, but no one gives a damn about it, so I thought I'd spread the word 'cause I haven't seen this posted anywhere else on the Google-friendly net. I'll just bluntly copy-paste here:
As you may know, nvidia released a few days ago a new beta driver for their gfx cards, the 310.33 beta. Well, in the change log there was one bug fix was that caught my eye - they repaired the "non-functioning MSAA anti-aliasing in Diablo III". I never got it to work previously, obviously because of the bug. And guess what? Now it works.
What has all this to do with framerate stuttering in Diablo 3 you ask? Well, as it turned out, by enabling even 2x msaa (override application settings) in the nvidia control panel, not only does the game look better with non-blurry antialiasing, it also (in a way I can't possibly comprehend) removes absolutely every single bit of framerate stuttering in the game! It's actually such a noticeable improvement, that I couldn't believe it.
I had that annoying constant stutter since the game launched (and I'm using an SSD, so there was no stuttering related to asset loading, I checked that quite thoroughly and by doing so learned the difference between these stutter types), and now it's gone!
This is obviously a fix only for nvidia users, unfortunately. I hope this info helps a other people too!
P.S. If someone needs the info, I'm running a Geforce 560 on Windows 7 64-bit.