That's cool. I guess a better question would be...what file format/codec is going to be the most cross platform compatible? I mainly shoot with the 5DmkII and then convert to Cineform. I'm wondering what workflow is best...what are my options?
The MOV files recorded by the 5D will work natively in both the Mac and Windows versions of Premiere, assuming a relatively robust system. You can then just bounce a project file back and forth and as long as you stick to the guidelines Todd linked to above, you'll be in good shape.
I don't use Cineform, but I believe there is a free player (Neo, maybe?) that installs the playback codecs on any system that doesn't have the encoder installed. That way you could stick with your Cineform workflow; note that you'll need to do your transcoding on whichever platform you have the encoder installed, and then you should be able to move the files to the other system and work with them there.
Ultimately, if there is a sequence preset for a particular format/codec listed in the new sequence panel of one platform, you'll have parity on the other platform and be able to work with it there. Third-party codecs, like Cineform, are going to require a little more user intervention.