A tip on the Tidbits site warns iTunes users of a password-caching "feature" that can can have unfortunate and expensive consequences.
Publisher Adam Engst tells the tale of designer Mike Rohde who logs into iTunes with his iPad. He buys an app and then as it is downloading, his 7-year-old son, on his own, proceeds to buy hundreds of bucks worth of apps. Oops.
This entire situation came about because of a design compromise. By requiring you to enter your iTunes account password for a purchase or free download, Apple ensures that an authorized user is in control of the device. That's a good thing. And by caching the password for 15 minutes, Apple reduces the significant annoyance of typing passwords (especially strong ones that include numbers and punctuation) on a virtual keyboard. In general, that's also a good design, although it can obviously have unintended side effects.
The feature, or problem depending on how you look at it, is Password Caching and Engst runs down the issue in detail. All iTunes users should be aware of the issue.