This tweak was reported to us by reader Blake some time back, but I've only recently had the chance to test it out myself. And, like most of the respondents in this thread, I agree that there's a noticeable improvement in framerate, though Blizzard poster Tigerclaw comments that the performance impact will really only effect those with heavy UI usage. The feature, added in patch 1.12.1, is designed for PowerPC Macs (the Intel systems already use "a better mode of optimization" according to Tigerclaw) with more than 512MB RAM, as it may add a couple of extra megabytes of memory usage. It's still considered a beta feature, but it's easy to enable and easy to disable if you have trouble with it. So if you run on a PowerPC system, give this a shot -- you may notice a 5-15% improvement (though some report even better improvements).