I use an old version (1.5) of utorrent with Vista. Downloading a video torrent in vista suddenly stops. I'm using the older version as I like it for its small size (200kb or so), and I read somewhere that some tracking bits were added to the newer versions (I can't confirm this right now). For some reason it seems that vista wants to create a thumbnail for the video, and this causes utorrent to stop downloading because another process is accessing the file.
Another problem I've noticed is that when I access a directory with a lot of media files, it takes a long time for the explorer to make thumbnails for the video, and the whole system seems to slow down. Further, if you want to delete items in the directory, updating the windows is slow, as its still trying to identify media files, create thumbnails and what not. This is really irritating.
In fact, their have been two occassions where explorer stopped responding and the system restarted explorer. This may also have to do with the codecs for the media files causing explorer problems.