Ben
My (admittedly limited) experience with PV 2012 so far suggests to me that the new PV is applying far too much highlight compression as part of the standard import profile. For a lot of images this amount of recovery is excessive, and I have observed (compared with 2010) not so much de-saturation, as you have, but odd hue shifts in the highlight areas. As I work mostly in B/W the colour anomalies are not of great importance, but I find that PV 2012 by default takes a great deal of the "pop" out of my monochrome images, and I find myself having to put it back in by boosting whites.
I would prefer a more linear import profile like PV 2010, and then have the option to use the undoubtedly more sophisticated highlighty recovery of 2012 if I so wish.
John