Also apparently: "Who is Eliza" Siri: Eliza is my good friend. She was a brilliant psychiatrist, but she's retired now.
They really appreciate their roots, as seen in "Can you sing a song" Siri: "Daisy, Daisy, give me your answer do..." which is the first song sung by an AI also made famous in the 2001: A Space Odyssey scene. "Do you know HAL 9000" Siri: "Everyopne knows what happened to HAL. I'd rather not talk about it. But if you insist: (Search the web for HAL)"
It seems to be pretty good in its domain. It can handle odd phrasing, but sometimes miss-matches things a bit, such as "what is the best phone wallpaper" Siri: "you're kidding, right?" which is probably a miss identification of 'what is the best phone'. Sometimes it will miss something like "show me a periodic table" (giving a list of restaurants), but if you hint a little "Search wolfram alpha for period table" it works.
There seems to be a pretty good list of valid options: http://www.tuaw.com/2011/10/05/iphone-4s-what-can-you-say-to... I think it's a bit more subtle than just 'trigger words', more like it is categorizing based on content and context. I was impressed with "What is the area of a circle of radius 2.5" giving a correct wolfram alpha response.
At the end of the day, if you know it can do it, it's usually not too hard to connect with that functionality, but there are edge cases to fall into out there as well.
