I hide the avatars and signature area on most forums. Several avatars and signatures include animation. I find the repetitive motion annoying/distracting and signatures are more to scroll thru. Since I hide the both, I rarely populate either.
Streaming a movie off to the side while in the forum is no problem - so it is not the motion that my mind objects to, the motion just cannot be near text that I read. I do the same thing when reading a news website, I shape the window to hide any animated things or scrolling banners.