It's about ten seconds after you empty the trash on your Mac OS X system that you realize you haven't had a successful backup for two months and that critical report for the boss is no longer on your Desktop. If it went into the Trash and you then emptied the trash, you're out of luck. Time to get some Red Bull and pull an all-nighter recreating the document.
Or is it? With the addition of Time Machine, Apple has a nice built-in file backup system that also helps with version tracking, but if you don't have it set up properly or simply haven't run a backup between when you created and accidentally deleted the file, it's not going to help you out.