I got one of the clear tank protectors fro the dealer when I got my bike. Parts of the adhesive that wasn't stuck to teh tank were collecting all sorts of sand and dirt. I saw the same thing when I took off the reflectors from the front fender. The protector ended up putting small scratches on the tank in those areas, probably from the protector being pushed on as I rode. You won't see it with your opaque protectors, but I can imagine the same thing happening under those tank protectors.
+1 for tank slapper, and the stuff is invisible. I like the way the bike looks without the doodads and other stuff, much cleaner.
I got the full kit and opted for the 3m stuff for the sheets that cover the tank (4 pieces: gas cap area, the back of the tank, and the two sides) because I got the two sides to start pealing off at the lower edges (where my knees rub) during rides (it's just stuck on by static, no adhesive). The 3M stuff is a bit harder to put on but it won't peal off because it has an adhesive back. the 3m is also tougher. It costs a few bucks more but worth it. My bug splat pic was right on the top fairing piece.