Even though Siri seems to be amazing I wonder whether people will use it much in practice. Voice is intrusive in the environment and annoying to people who aren't part of the conversation. Sitting next to someone conversing on the phone in a public space can be irritating but imagine how jarring it will be if the person next to you barks commands out loud at random intervals.
Him: "Remind me to pick up my dry cleaning."
You: "Huh? You talking to me? No..."
Later: "After picking up my dry cleaning, I want you to book me a flight to Tucson"
"You might wonder, Hey, don’t you feel like a jerk walking around the city talking to your phone? But here’s the thing: Siri, by default, kicks in when you hold the iPhone up to your ear, so you can talk to it and it looks like you’re on a phone call."
Him: "Remind me to pick up my dry cleaning."
You: "Huh? You talking to me? No..."
Later: "After picking up my dry cleaning, I want you to book me a flight to Tucson"
You: "I'm finding another seat..."