This isn't exactly a Mac type hint, but it may come in handy for those of you out there with kids.
There are a couple of options to clean a DVD or a CD. First, you can go out and buy a $30.00 to $50.00 dollar mechanical cleaner that uses liquid solutions and spins the DVD or CD and wipes it clean. Personally, I wouldn't want anything around that my kids could accidentally drink. When you run out of solution, you have to buy more. If the cleaner breaks, you have to buy another. Many cleaners are battery operated, so you have to spend money on those as well.
The second option is to, well, lick it. The enzymes in one's mouth do an phenomenal job of cleaning up little fingerprints that get on DVDs and CDs. I know, it sounds a little gross but it works. I've never had a DVD not play correctly after doing this and wiping it clean with a clean t-shirt or cloth towel.
I wouldn't recommend trying this with rented DVDs, nor after eating a bowl of Cheetos.
Erik