A lot of the examples show how you can text, email, or call using Siri by just referring to a person's first name.
"Text Vinny"
"Email Vinny"
If you have multiple Vinnies in your contacts, Siri will show you a list and prompt you to choose one. This makes perfect sense. However, the voice commands don't appear to work very well for choosing which Vinny. Siri doesn't seem to understand names very well ( which from a programmers point of view makes perfect sense ). I was hoping that it would work like most phone systems work however, where I could say "one" and Siri would select the first Vinny in the list or "two" for selecting the second Vinny and so on. It doesn't work like that. So you either have to click the "Vinny" that you want or try to say their whole name in the original request like: "Email Vinny Boombotz." And you have to really pronounce names phonetically ( not necessarily how they're pronounced ) to get the right name to show up.
The same issue comes up with email addresses. When you command:
"Email Vinny Boombotz"
If Vinny Boombotz has multiple email addresses, Siri will show you a list of Vinny's email addresses and prompt you to choose one.
I've found that text commands work better than email commands and that's usually because most of my contacts only have one mobile phone number and therefore one texting address. Saying "Text Vinny Boombotz" will have Siri prompt you for the body of the message. Saying "Text Vinny Boombotz I'll be right over" will have Siri put "I'll be right over" in the body of the message. Pretty handy.
Creating meetings and reminders works very well. When you say "Remind me to call Vinny Boombotz at 8:30pm" Siri will set up a reminder for 8:30pm with Vinny's number attached. So the reminder winds up with a "call" button on it for easy dialing.
Commands like "what's the weather today" and "show me today's meetings" are pretty handy as well.
Commands like "Find me an italian restaurant" have Siri locate italian restaurants local to you. Clicking on one shows a map and then clicking on the map label will show you the phone number and address of the restaurant.
There's a whole slew of mapping functions that I haven't even tried yet.
The Wolfram Alpha piece of Siri is kind of like the ultimate bar bet tool. You can ask questions like:
"Who won best actor in 1982?"
"Who won the SuperBowl in 1986?"
"What's the population of China?"
"How many calories in an Egg McMuffin?"
And the Wolfram Alpha piece kicks in and gives you a handful of information on your topic. Again, if its not in Wolfram Alpha, then it falls back to a web search. But I found this much quicker then typing in a search. I'm probably going to use this piece of it quite a lot.
There's also a bunch of fun questions you can ask Siri that I mentioned here.
There's big things missing from Siri right now that I hope get improved. There's really no concept of "latest news" or "latest baseball scores." Siri will prompt you to do web search for these terms. Ideally, they should open up the API to/from Siri so that if you ask for "latest baseball scores" it can query ESPN or another sports outlet for that request. It would be really killer if when you created iphone apps that you could register some Siri answers in your app so certain questions would go to your app instead of just a default web search from Siri.
So in the baseball case, the ESPN app could register answers with Siri to questions like "Latest baseball scores" or "Next Texas Rangers game." So if Siri couldn't find the answers to those questions, it could question the ESPN app on your phone for those questions, before doing a default web search.
In conclusion, I think Siri is a nice addition to the iphone. It's not quite a killer app but its definitely useful and something I'll probably be using a few times a week.