Most of my professors distribute powerpoint slides prior to lecture. However, I prefer to use keynote so I created the following Hazel action to convert from ppt to key format:
if the extension is "ppt" then run this applescript:
tell application "Finder"
set theDestinationFolder to container of theFile as Unicode text
end tell
tell application "Keynote"
open theFile
set theSlideshow to slideshow 1
set theDestinationPath to theDestinationFolder & (name of theSlideshow)
save theSlideshow in theDestinationPath
close theSlideshow
end tell