Both scrolling while sites are still loading and scrolling after sites are fully loaded has gotten slower for me. Scrolling was always choppy while sites were loading, but it's pretty terrible now.
As far as I can tell it affects all websites, although sites with more images are affected more. Even simple sites like Boston, Massachusetts (02110) Conditions & Forecast : Weather Underground for iPhone are slightly but still noticeably less smooth. Other sites like The New York Times - Breaking News, World News & Multimedia are quite obviously choppier.