So yeah, after hesitating a bit mainly due to reading about various artifacting/aliasing problems, I have just installed LR 4.1 RC2. I have obviously not had a lot of time to play with it, but I thought I would start a thread here with a first couple of test results. One of the main features of this upgrade is the introduction of more advanced controls for fixing chromatic aberration issues (and apparently this is also the cause of the main issue as observed below...). It seems the new controls (a couple of sliders that let you chose the amount and hue of purple and green that is corrected around edges and other places where chromatic aberration typically occurs) do work better than the previous version's simple "on/off" switch for CA - check out "4dot0test.jpg" vs. "4dot1rc2test.jpg". In the 4.1 version of the same picture, you can see that LR has removed pretty much all of the purple fringing in between some of the colors (some of which is still visible in the 4.0 version if you look closely). It has also done a better job of keeping ALL the original colors in there...notice how the black band around the big blue areas top right has all but disappeared in the 4.0 version, but it's still in the one created with 4.1. Other settings were kept the same between the 2 exports.
Now for the bad news: the artifacting issue is real. If you look at the second set of test pictures ("artifacting_4dot0test.jpg" and "artifacting_4dot1rc2test.jpg"), you can see that although 4.1 has done a better job of getting rid of the purple (visible on the small branches in the 4.0 version), it has also completely messed up the surface of the thicker branch, full of ugly white stripes. And this was with the clarity slider at 0 (I have read elsewhere that people have seen this artifacting caused by the clarity slider, but it seems to me that it is caused by the CA treatment...).
Other than this issue, the import of old catalogue and the general upgrade went smoothly. It would also seem less prone to crashing at this point although that needs more testing before come to any conclusions.
Anybody else out there with experience of these issues? Anything else to report on this upgrade?