JTFoto,
Chris is out of the office today, so I'll jump in.
From my point of view (doing Capture One Tech Support) the two major improvements are:
• Occasional black lines running Leopard (10.5.x)
• Default capture format is now IIQ Large
So if you're already stable and have never experienced the black line problem in Leopard (it was a rare and machine-specific problem) then I see no reason for you to upgrade. Keep in mind that for 3.7.8 anytime you dump preferences, reinstall, or install for the first time you need to change the Capture File Format (preferences > camera setup) to IIQ Large or IIQ Small. 3.7.9 eliminates the need to do this.
You probably already know this but Capture One 4.1 has a feature called "export to web gallery" which creates an HTML / javascript webpage-contact-sheet with thumbnails up to 240px and previews up to 1000px. For a folder of 100 images on a fast intel-based tower it should take on the order of 20 seconds (that is total time, not per image). The only drawback here is that 4.1 won't read your adjustments from 3.7.8, so if your primary workflow is 3.7.8 then this is not a great solution for you.
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I'll check on the Preview Converter now. If anyone beats me to it feel free to post your results.
Doug Peterson
Capture Integration, Phase One DealerPersonal Portfolio