It does do a sync on quit, and may also write a backup, depending on your preferences, which might take even longer if a disk has to spin up. That said, it takes OF about 4 seconds to quit with my 7500+ action, 8.5 MB database if a disk doesn't have to spin up and the sync isn't one that causes a database compaction. The code may be clever enough to not do a database compaction during the sync on quit, I'm not sure, but I know it takes a while to write that much data to the cloud. If it always takes 20+ seconds to quit, I'd say there is something amiss with your setup, and you should have the support ninjas help you figure out what it is and how to fix it. 800-315-OMNI, +1-206-523-4152 or
omnifocus@omnigroup.com should get the ball rolling.