I'm livid. I decided it was time to get back into Starcraft 2 after not playing for a few months while I was away. But much to my chagrin the game now feels like it's being run on a Power Mac 8600/300 instead of my high-end Core i7 Radeon HD 5850 system (and that's not meant as a knock against the Power Mac btw). After a flurry of reinstalls and troubleshooting, I've realized that Blizzard has ruined Starcraft 2 for me and everyone else with similarly configured systems by not doing proper QC on a recent patch. The at-fault patch apparently got pushed out in September some time. It took me a while to find it, but here's a thread reporting the problem I'm having:
Sc2 suddenly very laggy
At first I blamed the problem on the Nvidia PhysX component that my brother installed while I was away for some games he plays, suspecting that it could cause problems with ATI graphics cards. Wrong. I then reran the Windows Experience benchmark to see if my graphics performance dropped somehow (which would be impossible given that much more graphically intense games are running wonderfully); the graphics scores actually increased from 7.5 to 7.7, apparently because of driver improvements. After much scouring of Google I finally got the confirmation I was looking for that this wasn't just confined to my PC. This is ridiculous.
I've never had a problem like this with a Blizzard product, or any other game update that I can recall. If Blizzard doesn't get this remedied soon I'll go on some sort of rampage!