I just upgraded to MacOS 10.7.4 and upon restart Capture One 6.4 crashes on startup (MBP latest generation). There is nothing special about my setup, never used the FileVault (which had security bugs that are now supposedly fixed in 10.7.4). Clearly something else has changed as well. Really weird, just wanted to post a warning here. At least make sure you have a bootable backup before you attempt this "upgrade".
I had to restore from my 10.7.3 boot image. Would be interested in hearing if others have the same problems.
PS: There is a C1 6.4.1 upgrade available from PhaseOne as well. I did not try that, but according to the release notes it's basically just new camera support.