Here's an interesting take from Searchblog's John Battelle about the Siri purchase by Apple yesterday: he believes that it's the first step towards the eventual Apple goal of conquering search for the app world. Google is, of course, the king of search on the Internet, but as the iPad 3G releases today, we're spending less and less of our time on these devices actually browsing the web, and more and more of it inside of apps. That's where search needs to go, says Battelle, and Siri could help exactly that happen for Apple.
In other words, he gives the example of searching for a phrase like "Chicago rental car" in Siri, and properly configured, Apple's Siri could say back to the user, says Battelle, "Hey, you know what? You don't need to rent a car. You can use the Chicago Transit. Here's an app for it. You can get from the airport to everywhere you want to go without having to rent a car. Plus, you'll save $150 which we know is a goal of yours because you've been interacting with the Mint application," and so on. Siri would become a voice-activated search assistant, not for the Internet at large necessarily, but for all of the apps and functionality on your iPhone or iPad.
It's certainly possible, although Apple has so much cash saved up right now that they don't really need good, focused reasons like that to pick up a strong piece of tech like Siri. But yes, Battelle's guess makes sense, especially considering the increased amount of time that people are spending in apps versus the browser on the iPad.