How to Check Authenticity of an AJAX Request

I am designing a web site in which users solve puzzles as quickly as they can. JavaScript is used to time each puzzle, and the number of milliseconds is sent to the server via AJAX when the puzzle is completed. How can I ensure that the time received by the server was not forged by the user?

What happens when there"s insufficient memory to throw an OutOfMemoryError?

I am aware that every object requires heap memory and every primitive/reference on the stack requires stack memory.

How unique is PHP"s __autoload()?

PHP's __autoload() ( documentation ) is pretty interesting to me. Here's how it works: