"A middle school science teacher in Seattle, Justin Baeder, wondered whether he saved very much getting his DVD's through the mail. So he created an Excel spreadsheet that calculates exactly how much he does save. It turned out to be just a little, about $6 a month, but he loves Netflix and keeps using it.
He's posted the calculator on his Web blog, the Republic of Geektronica at www.geektronica.com. All you need to do is download it and paste your Netflix rental history, which Netflix provides on its site, into the spreadsheet."