If you haven't done anything with acetate, you really need to give it a try. I prefer the 10 mil thick variety, as it makes the card seem a little more substantial. The cat card in this post (cat stamp by Penny Black, flourish by Impression Obsession) uses acetate as the base card. The flourish is stamped with pink opaque Stazon. The trick with a card like this is that you need to adhere some cardstock on the inside of the card for inside wording. It is best placed behind the front image. You also have to remember that the adhesive on the lowest layer will be visible through the acetate. I prefer to use a Xyron for this.
The snowman card (stamp by Darcie's) has 10 mil acetate run through a Cuttlebug embossing folder. This gives a wonderful effect and does not alter the size of the cut acetate.