I recorded a comedy show from German TV, and when encoding it with Theora the background smears horribly. This is probably caused by the background being a blurry play of blue-green colors without well defined features. With Theora, the pattern is smeared and when the camera moves, the background looks like something trampled over it. The original TV recording is more noisy, I scaled it down. I never attempted to encode the original, only the scaled down version. In the scaled down version there is still some noise left on the background.
I have reencoded the video with mencoder to an AVI with H.264 and MP3 and uploaded the video to my web server. Try transcoding the video with ffmpeg2theora to see the effect. I deliberately encoded the H.264 version with a high constant quantizer.
Here is my source material (~ 38 MB):
and here is what I get from ffmpeg2theora --optimize (~ 20 MB):