For a lot of internet based tasks, I can open the phone and find out more comprehesive information just as fast (if not faster) as Siri. But...
The Reminders App is GREAT, but manually entering them in, then going to set a alert for the Reminder is such an annoyance and SIRI can do that WAY faster. So I use SIRI for reminders, alarms, and use it to help me in my car through my cars hands free system.