In my case, I turned it from "Application Preference" to "On" in the Control Panel. No changes in fsx.cfg.Just make sure that there is not some kind of over-ride in the Control Panel application presets..The effect was dramatic, first: wavy scenery updates when I banked the plane and after: rock solid scenery just as it was prior to Acceleration.

Bert ...I am turning on VSync as you directed with no fix in DX-10. Is your "fix" experienced with DX-10 preview or DX-9 only? My DX-9 is fine. My problem is only in DX-10. I'm going to e-mail you this question.Thanks, Steve

This condition is known as "tearing".http://www.tweakguides.com/Graphics_9.html