QuickLook doesn’t work with Chat transcript files

Trying to use QuickLook for Chat transcript files isn’t working anymore on my machine. First it takes >10 seconds to load (for files <20KB) - and then when it does finally load, it’s just an icon. I can’t actually read the chat. Anybody else having this experience? I’m not even quite sure what to try resetting! Deleting the QuickLook plists does not seem to have changed anything.