I am having the same problem. When I first installed Debut Pro I was able to watch smooth video while recording. I don't know what changes I made but the video recorded with Debut is unusable. I wish there were some kind of manual available that would explain the way to properly set up Debut. So far, I consider I have wasted my money.
I am very disappointed with the fact that Debut does not seem to be able to capture 16x9 HD as I bought it believing it would. I did lots of tests using Debut Pro and my BlackMagic Intensity Pro Capture card. Debut recognizes my capture card and works very well. However whenever I capture video from either of my three HD satellite receivers I end up with a letterbox picture. Unless I don't know how to set up Debut preferences, my conclusion is that it cannot capture full 16x9 video. I would be pleased to be proven wrong. Thanks