I got the same stuttering/fps issues as well (along with tons of other people). Not sure what is the problem but I did a fresh format the day Sc2 was released, latest drivers for everything, variables.txt overheating fix, etc, etc. Stuttering happens no matter what graphics setting and it is extremely frustrating.

Looks to be a software problem, even those with high end machines are having this problem so its quite bizzare. Hopefully blizzard will fix this so the rest of us can enjoy this game