http://www.youtube.com/watch?v=SHoukZpMhDE&feature=share
Gives an idea about the capabilities of each....though I am not sure if the person who did the video picked phrases he knew one would mess up or what not
Even if he did, that just shows Siri is capable of recognizing a wider range of commands than competing software. Personally, I don't think the commands were too far fetched. Things like "send a text to" or "what time is it in Perth" should not have been too difficult for voice recognition software, yet the Windows phone didn't even understand what was said. It interpreted "sent a text to Simone" as "stain detector simo." That's not even close!
I think the first example where he tries to create a meeting shows just how far ahead of the competition Siri is. When he said "create a meeting tomorrow at 10 AM" the Windows phone got "create a meeting tomorrow at 10 anal" (lol) and tried to do a web search. Meanwhile, Siri understood what was said, created a draft calendar event, and pointed out that the proposed event conflicted with an existing appointment before asking for further instructions.
Siri is definitely not perfect, but it is lightyears ahead of the voice recognition on Windows phones.