I've been a regular viewer of this forum and it's given me solutions for several issues I've had with my set up over the past couple of years. I've joined so that I can return the favour by relating my experience of this frame judder issue.
I first noticed this problem around the time of the BBC televising tennis from Queens (I'm not a great tennis fan but I found the judder was particularly noticeable during these broadcasts), however the judder could be seen continually during any programme, even upscaled ones, on BBC HD channels. It didn't occur on any other UK high-def free-to-air channel (either DVB-S2 or DVB-S). A search of the web found only the older Freeview BBC DVB-T2 25/50 fps switching issue which I assume is still unresolved and this seemed to be associated with the even older but virtually identical 29/60 fps "bug" issue being experienced in the US.
Have a look at this for an excellent explanation and suggested workaround: http://experts.windows.com/w/experts_wiki/71.aspx
Certainly if you debug (by 4-1-1-Info) you will see the frame rate momentarily flicker from the usual 50 continually throughout the broadcast and it usually corresponds with the judder. It's such a brief drop from 50 fps, it's difficult to actually see what the momentary fps is (I think I saw 25 a few times and a member of my family thinks she saw 49 "point something", so it might be all over the place). Do the same debug for a non-BBC DVB-S2 free-to-air channel (or any DVB-S SD or HD channel) and the fps stays a rock solid 50 (I referred to http://www.lyngsat.com/Eutelsat-28A-and-Astra-1N-2A-2F.html
to show which high def channels are using DVB-S2 since some HD channels such Channel 4 HD and some ITV HD versions are using DVB-S).
You will see from the wiki above that the workaround has been to try one of a small number of GPUs immune to the issue. I was using a Radeon HD 6570 on my Media Center but was able to swap it with an HD 6450 being used on a different PC in my house. Since using the HD 6450, there seems to have been a 99% improvement. I'm reluctant to say 100% as I occasionally notice the odd extremely slight stutter - absolutely nothing as bad as before and nowhere near as frequent - but that might be simply because I'm casting an excessively-critical eye at the screen since the problem began (no one else in my family seems to think there is a problem since the change of GPU).
I'm sure a change of GPU isn't going to be welcomed by many users and I wasn't too happy downgrading from my HD 6570 however I found the perpetual juddering was making BBC HD channels unwatchable and I'd already invested too much time and money in my set up to have to go back to using set top boxes. Clearly the source of the problem is the BBC and I suspect an unadvertised change on their part has caused this however, assuming the similar issue with DVB-T2 remains unfixed, I guess the reality has to be the workaround as our only option.