More Mac 101, our series of tips and tricks for novice Mac users.
This isn't so much an actionable "Here's how to accomplish X" sort of Mac 101 as it is a "Aha, so that's what's going on there" reminder. If you've ever been prompted by one of your favorite applications to download and install an updated version, chances are you've been served by the Sparkle framework. Andy Matuschak's open-source updater code is at work in hundreds of Mac apps, saving you the aggravation of having to go and track down new versions yourself. It's a beautiful thing.
One of the nice features of the Sparkle approach to updates is that the code gracefully moves the old version out of the way when the new version is installed. Those old versions may wind up in your Trash, and if you have a program like Webkit installed (which commits new versions every night) those expired builds may soon represent a sizable bit of disk space. A quick Empty Trash will take care of the old stock. (If you're an iPhone or iPod touch user, the .ipa files accumulating in the Trash are the previous versions of your installed iPhone apps.)
If your Trash is sporting several programs (as in the screenshot above), but you don't remember throwing them away, don't worry; you're just staying current.