Siri is great and for me, it was worth upgrading from the iPhone 4 to the iPhone 4S to get it. But don't be fooled by imposters.
For example, there's an app named "SIRI" that has NOTHING TO DO WITH VOICE CONTROL. Somehow, the app was approved, on October 13th, and is doing very well in the U.S. app store, despite the fact that the description and app aren't even in English! Indeed maybe that's the trick. People can't tell what the app does, so they get it and end up disappointed. I won't link to the app, because it doesn't need the extra accidental sales, but here are some screenshots that give you an idea of what the app does and how customers have duped themselves.
As a developer, I'm torn, because this demonstrates that people will search for an app by name or keyword and simply buy it. I suppose I've benefited from that purchasing style. But it also results in customer dissatisfaction and Apple is going to have to deal with it in refund requests. So for now, buyer beware and read those descriptions and reviews!