Have you downloaded Lightroom 4.1 yet? If not, you're really missing out. Check out this shot:
This was shot with a Tokina 10-17 fisheye. I am working on a review of that lens but for now note that the Tokina fisheye is very susceptible to purple fringing and chromatic aberration:
Lightroom 4 includes a command to Remove Chromatic Aberration but Lightroom 4.1 takes this further and adds an additional tool for removing aberration: the Defringe tool. It has an eyedropper and all you do is click on any purple or green fringe color. Check this out:
Boom! Gone in just one click!
If you look closely there is a little bit of green fringing. Just click the eyedropper a second time, this time on green fringing.
Now both purple and green fringing are gone. Tokina should include a copy of LR 4.1 with every lens they sell! :)