Siri is a personal assistant that interprets your speech to perform common tasks. You can ask Siri to make restaurant reservations, find movie showings, check flight status, recommend weekend activities, and more. Indeed, there's a treasure trove of things Siri can do, and I've had a blast for the last few days trying to stump it. More often than not, I wasn't able to.
I've been impressed to discover that Siri can parse fairly complicated sentences -- you can ask it to find a specific kind of store in your local area (it's location aware, naturally), locate Mexican restaurants, or find a theater where you can watch a specific movie. It can't yet book a flight for you, but Siri promises that feature is coming soon.
This is the first time I've seen a program that pairs speech recognition with personal assistance, and the broad range of Web services -- over two dozen right now -- means it's actually useful. Check out the video, and then grab Siri for yourself -- it's free.