Mac Cheat Sheet
Unless you're the sort of person who wouldn't remember this information in the first place. So you'd probably keep the sheet on-hand, right?
Admittedly, the form contains all the information that could really help a service tech: which OS you're using, the amount of memory in your computer, and the kind of processor. But it also details your user account password, up to three keychain passwords, a password for your ISP, passwords for your email account, your work account, and so forth. This is offset by six light gray repetitions of the phrase "don't forget to hide me", which I guess immunizes Apple from losses due to security breaches.
So bottom line? The cheat sheet is a well-intentioned idea that, when used as intended, could really help during service calls, but when used in its most likely scenario will introduce unacceptable security risks.
Remember the first rule of computer security? Not writing down all the important stuff like passwords and account names in one place? Kind...