I talked to Dynastar/Look today and received some interesting info from a manager that might be useful for others in the future. This post archives this tidbit of info that so that people might be able to access it in the future.
He told me that the total mass difference between a pair of Look PX12 and PX12 Ti of comparable feature (ie. PX12 Jib vs. PX12 Ti Jib, PX12 Lifter vs. PX12 Ti Lifter) is ~40 grams, which is about ~1.5%. The difference is completely negligible. (No, I didn't catch which version was actually heavier. Waxman's prior post indicates that the Ti version is heavier: http://forums.epicski.com/showthread.php?t=29287)
He then proceeded to tell me that the difference lies in the lateral rigidity of the heel, with the Ti version being noticeably more rigid. This makes sense to me since the material upgrade is obviously in the heel riser arms.
I asked him to volunteer his opinion on whether this would make a difference for my newly-purchased pair of K2 Public Enemy (PE)'s. He said, "probably not, since most mid-fat twins aren't that torsionally rigid. I'd save the $50 bucks."
I think we can take the first two statements as fact-ish, and qualify the last one as YMMV.