I bought Glue Tools' Cineon/ DPX Toolkit for Mac OS X and used it with Compressor 4 on my Macbook Pro.
I was able to Convert Log Cineon Image Sequences into ProRes 4444 XQ QuickTime Movies.
Some things to note:
After downloading the Toolkit, you have to activate it from your System Preferences Panel, and make sure that you select the correct Conversion Settings in the Cineon/ DPX Icon (at the bottom of the System Preferences Panel).
They also have a Trial/ Demo Mode for you to try out.
Gluetools Cineon/DPX Toolkit (4.1.2936) currently supports only Compressor 4, but may add functionality for FInal Cut X and other tools in the future.
Use "Import File" in Compressor 4 and select the first file of the Cineon or DPX Image Sequence when you're trying to get Gluetools to read them in. Don't use "Import Image Sequence".
Once you're written out the ProRes 4444 XQ, you may still need to Color Correct it, but Gluetools has excellent support.