I had this problem a few weeks after I updated to Lion. I used to be able to play movies and music and turn PDF pages from the icon thumbnail itself by clicking a small play button on the movie or music thumbnail, or flip through a PDF document using small directional buttons appearing on the PDF thumbnail itself without tapping the spacebar for Quick Look, or actually opening the file itself. Somehow, I lost this functionality now without knowing how or why. It was pretty useful when you want to hear audio in the background without using any apps (iTunes, Quicktime, etc.) Has anyone encountered the same issue before?