I use Siri constantly:

- change playlists when when I'm working out or biking

- set the alarm when I go to bed

- reminders (a lot)

- the weather

- looking up something on wikipedia and imdb

- and sending short sms messages

I'd say my use has grown over the last few weeks as I'm biking a lot more. There was an initial trust issue, and I still sometimes have this weird feeling of being on the spot when I'm dictating to Siri, but otherwise best "app" on the phone for me.