However, I really like it when driving, so I don't think it's entirely a gimmick.
I thought it was a recent acquisition?
Wikipedia claims April 2010: http://en.wikipedia.org/wiki/Siri_(software)
Me: Will it be cold tomorrow?
Siri: Not too bad, the low temperature will be 57 degrees.
Me: How about Saturday?
Siri: Looking colder, the low temperature will be 34 degrees.
It is my second question that is the hard part. Siri "knows" that I'm still asking about the temperature, despite no reference to temperature in the text of my question. OS X and previous versions of iOS cannot do this.