I've been intrigued by the threads here on synthetic vice dyno juice. This past weekend, I converted my 82 300SD Turbodiesel over to Amsoil S3000 diesel rated synthetic. Flushed it out with their flush, drained and renewed with the Amsoil. I'll keep posted on whether anything happens plus or minus. My car has about 220K miles on it and has been using a little bit of oil, less than a quart every 3K miles.
I'm also interested in any experiences with the bypass filters. The Amsoil literature really makes a good case for this, but it would require some modification - removing the oil filter canister and replacing it with their custom 2 filter setup. But their literature makes it sound as if engine wear will be brought down to essentially zero, with the other benefit that one can go long times between actual oil changes.