Think Secret first reported that Apple is migrating to a new 18-digit all numeral serial number format (from 9 alphanumerics) for all of their hardware, including iPods, desktops and notebooks in order to accommodate the explosive growth in Apple sales. The article goes on to say that "sub-assembly parts, such as optical drives and logic boards" will move from 12 alphanumeric character serial numbers to 17 alphanumeric characters.
Chipmunk International has posted a decoder ring for Macintosh hardware serial numbers. Simply enter your SN into their online form and it will tell you all kinds of facts about your Mac including: name, model, production factory, production year, week and number during that week. The site supports all Apple products including computers, laptops, monitors, printers and batteries.