Apple's criteria for upgrading to Mountain Lion is whether you own a mid-2007 or newer iMac or late 2008 aluminum MacBook and so on. I mean, what? I don't see dates like that when I open my MacBook's About This Mac info window. Newer MacBooks are showing this type of year-of-production info, but not the old models. Hence the value of this German web site dedicated to Apple tech support. Enter your serial number for various Mac products (computers, laptops, printers, batteries, and monitors) and it will extrapolate various bits of basic information, such as the item's manufacture date, model number, and so on.
This can be useful info for people like myself who want to know whether our products are eligible for the upgrade to Mountain Lion. Alas, my poor little plastic MacBook is mid-2007, so I'll be staying with Snow Leopard for quite a while yet.