Actually, screen protectors have minimal if any impact on the Tablet's active digitizer - I had one on my M200 for years with no issues. I haven't put one on my new Gateway (with one of the really shiny screens) because I haven't found a widescreen protector made for it yet.

Not sure why your Fn+Light Bulb key isn't working - you don't say which Tablet PC you're using. Works fine of my M200 and my new Gateway S7200c. At the risk of being obvious, have you checked at your OEM's site for a driver update?