I have a set I bought them and never bothered putting them on until after one long ride when a couple of chain ring bolts on my XTR crank set loosened and I ended up chewing the crap out of the rings as they wobbled back and forth, unbeknownst to me.
I put them on, and after fiddling with them for hours to get the repositioning and adjustment of the front changer just right, I got them working fairly well. The biggest positive I found is that shifting rings is much more positive than before. I rarely miss a shift... one click on the lever and boom, the chain shifts.
I honestly can't say whether I've noticed a performance improvement or not. I have noticed, however, that when I lock out my rear shock there is quite a sensation of bobbing/surging, but when the rear suspension is active, everything is smooth. It makes me wonder if the suspension is absorbing the power that the rings are designed to create and negating the benefit. Hard to say.
Regarding the comparison to Biopace, from what I understand, the power position of the Q Rings is in the opposite position to Biopace, so they really aren't comparable. There is about a 90 degree difference in where the tallest part of the rings are, between the two.