LR 4.1's speed is making me want to blow my brains out! Not only is the program slow to respond and show changes when using the brush tool (now count slowly - 1, 2, 3, 4...), but the interface is a slug. I move a slider and it's the same 3-5 second count -- and usually I've moved too much. I've taken to entering values manually -- faster and more precise. I love the quality of output (I also own DxO 7.5 and Capture One 6, but I keep going back to LR), but this makes me think about trying out Corel's version of Bibble (which I also own..). There are times I feel I waste far too much time waiting for the program to catch up with any move I make. My system isn't slow: AMD Phenom II x6 1100T (six core obviosuly), 16GB of RAM, an SSD for scratch disk and cache, a fast video card, 2 - 24" NEC Monitors, tons of fast external drives. If my system, which is no slug by the minimum standards (and even by more advanced), they've got some major programming issue. I just pray PS CS6 doesn't have the same snail's pace.
As for comments regarding the use of the GPU/OpenGL, I too feel it's overrated. I have OnOne's Perfect Suite. Most of the plugins, while good, are slugs because they use the OpenGL. I use to use Genuine Fractals. I've basically stopped because of the speed issue of redraw. I now use Alien Skin's Blowup 3. Faster previews and actually better enlargements.