I have printed black and white line drawings on acetate and used art glitters on the back.
Also if you use paint effects on card it looks effective to print out black silhouettes on acetate to mount over the top. I have also used the black outliners from Rainbow Glass to trace silhouettes on acetate too. These look nice over layered paper effects.
Sponge acetate with glass paints, glitter glue etc and punch out really lovely translucent shapes to decorate cards.
Ooooh yes and you can making simple horizon type shapes (mountains, grass etc) and using them to chalk up backgrounds. Because they are on acetate you can see exactly where you are positioning them, you can reverse the shape and they last a long time too.
Hmmmm I like acetate, don't I? *grin* (Don't get me started on coloured acetates!!!)