I've only had Siri on my iPhone for a few months now. I upgraded from the iPhone 4 straight to the iPhone 5, so the first time I got to use Siri on a day-to-day basis was with the iPhone 5. And Siri is pretty awesome. I tell her all the time. And she tells me how awesome I am — at least when she actually works.
There are two big reasons to use Siri: One, to set reminders for yourself, and two, to schedule events on your calendar. These are two things that become way faster with Siri than doing them by hand.
Reminders and Siri
Now, scheduling just a basic, time-based reminder using Siri is no biggie. Just tell Siri what and when to remind you.
But did you know that you can schedule a todo without a specific time? Instead of telling Siri "Remind me to do x-y-z" (followed, presumably, by a time) you can just say "Remember to do x-y-z". Now Siri won't prompt you for a time for this reminder and will just add it as a regular todo item.
Why would you want to do this? Well, now you can tell apps like Things or OmniFocus to auto-import all of your todos that do not have a time associated with them, and leave the ones that do. This way you can use Siri to create all of your reminders, but leave the actual Apple Reminders app only to handle time-based reminders, while all of your other, more general todos will be pulled in my your task manager of choice.
Events and Siri
Scheduling events with Siri is simple enough. Just tell Siri all of the required information and you're done. Actually remembering these events is a different story. That's why I like to set an alert 15 minutes before any event I put in my calendar to remind me that I have to, you know, actually go to it. I also have all-day events remind me the morning of.
But how can you set these reminders with Siri, you ask? You can't, actually. But fear not — this does not make Siri useless for scheduling events like you might think. You see, you can go into the settings on your iPhone, then into the section for "Mail, Contacts, and Calendars" and from there (if you scroll to the bottom for the calendar settings) you can set default alert times for both time-specific and all-day events under "Default Alert Times". This is probably something you'd want to do even if you don't use Siri for event scheduling as, if you're like me with the event alerts, this will probably save you a step every time you create a new event.
And isn't that what all of this is about? Saving time?