I think Siri's usefulness really depends on your location: In the office - hell no, people will think you're a tool. At home - sure, the kids love it! In the car - absolutely, to do all I can while traveling.
I actually had no expectation of using Siri given the fact that the last "Voice Command" feature Apple rolled out was an utter joke. However, in the car while driving, Siri is indispensable.
I use a bluetooth in the car (since it's the new law) and I find now I can read my texts (or have them read to me), reply to text, send a new text, send email and make calls without removing the phone from my pocket. It's awesome! Best part is, it actually works! I honestly never thought I'd use Siri but she's proving to be a great companion in the car.