Quick Powerpoint preview on Mac OS X

Macosxhints provides a nice solution that I have only slightly edited here

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1. Navigate to /System » Library » QuickLook » Office.qlgenerator. Control-click on the generator and pick Show Package Contents from the pop-up menu. Then navigate to Contents.
2. Create a copy of info.plist to use as a backup.
3. Change write permission of info.plist
4. Open info.plist with TextEdit or your favorite text editor.
5. Scroll down to find the following text:
      <real>800</real>
        <key>QLSupportsConcurrentRequests</key>
        <true/>
        <key>QLThumbnailMinimumSize</key>
        <real>17</real>
      </dict>
      </plist>
6. Replace all of that with this:
      <real>800</real>
        <key>QLSupportsConcurrentRequests</key>
        <true/>
        <key>QLThumbnailMinimumSize</key>
        <real>17</real>
              <key>UTImportedTypeDeclarations</key>
        <array>
          <dict>
            <key>UTTypeConformsTo</key>
            <array>
              <string>com.microsoft.powerpoint.ppt</string>
            </array>
            <key>UTTypeDescription</key>
            <string>Full screen PPT file</string>
            <key>UTTypeIdentifier</key>
            <string>com.microsoft.powerpoint.ppt</string>
            <key>UTTypeTagSpecification</key>
            <dict>
              <key>public.filename-extension</key>
              <array>
                <string>pps</string>
              </array>
            </dict>
          </dict>
        </array>
      </dict>
      </plist>
7. Save the new plist file and quit the editor.
8. Navigate to your user's Library » Preferences folder, and trash com.apple.QuickLookDaemon.plist.

et voilà

screenshot