Siri can be great for hands-free use of your phone, but a recent experiment by Apple Analyst Gene Munster shows that if you can use your hands, you're better off just typing your search into Google.
Siri's more than just a voice-activated search engine -- it can find movie showtimes, Yelp reviews, and a whole lot more. Unfortunately, those things can also muck up your search results a lot of times, since Siri often gives them precedence, even when the question you're asking doesn't match the situation. For example, if you ask about when a movie came out, it'll give you a movie theatre search instead, or asking about an upcoming event (like Haley's Comet), Siri often searched your own calendar for meetings. Google gave the correct answers.
Obviously, this doesn't mean you should discount Siri altogether. Instead, learn which things Siri is good at and user her for those things if you want to -- but for now, Google is probably a better go-to option. Hit the link to read more about the experiment. It wasn't perfect by any means, but it does bring up some interesting points about where Siri's faults and strengths are.