When I'm on my way out from work, I like to tell my wife that I'm on my way. But that usually involves me sitting in the car, waiting for her to answer her phone, or attempting to type out a text message while trying to not walk in to anything on my way out to my car. I'm in a hurry - I want to get home! So it'd be nice to tell my phone to notify my wife on my behalf.
Also, it's annoying to "look something up" on a phone. For instance, if I want to know how many career yards LaMichael James has, I have to open up my browser, start a new page, click on the google search box, type in everything, letter by letter, and clicking X on any autocorrects that come up because it hasn't heard of the name "LaMichael" before. It'd be so much easier (and faster) to just say it, and it give me an answer right back.
Who knows, maybe I'm dreaming and I wouldn't enjoy/use it as much as I think I will, but only time will tell... but the only point I wanted to make with this thread, is that Siri is VASTLY different from any previous voice command systems built in to an OS.