I'm a student and and I'm counseling intern (with a dozen clients and two groups). My university is pretty big, a lot of hills, and the main walkways are crowded with people during the middle of the day. I also have to walk through the college town a lot to get to different bus stops, work, or to the campus shuttle.
I have a pretty packed schedule and quite frankly, I spend most of my day walking. I'm on the go all the time and it's not safe to be walking and typing to search for a phone number, send a quick text, look for an address, make adjustments to my schedule (that my supervisor follows for safety purposes), or set reminders that help me manage homework, housework, and tasks I have for my internship. I have a lot of tasks and ideas to juggle (ideas for homework, activities to do with my clients, household stuff), so as I walk across campus, I just activate Siri and speak through the mic on my earbuds to record it in my Notes or Reminders very quickly. I've had the iPhone for literally less than a week but I've liked how it's help organize my day immensely.
Honestly, I think it really depends on your lifestyle. On days when I'm completely work-free I can't imagine myself using Siri a whole lot unless it's to set an alarm.
