I'll be the detractor in the use category. I use Siri all the time on my iPhone, but I feel it's important to make that distinction. I would most likely never use her on iPad and theres a few reasons why, but the main one is I own an iPhone.
My iPhone is ALWAYS on me, and that means if someone wants to set up a meeting with me, give me their contact info, I want to change my work calendar, or I need to set-up a reminder to pick up bread on the way home from work tonight I'll whip out my iPhone and Siri will do my bidding. Consequently all my other iOS devices (my iPad for example) as well as my home Macs will get that same meeting, contact, schedule, or reminder. In a way my secretary, Siri, has taken care of all the grunt work just like a real secretary would have. How likely am I to want to do any of that with my iPad that is A) not always with me B) usually in a bag or a briefcase when it IS with me C) 10 inches big, so big I'd look like an idiot holding it up and talking to it? And yes this is also a passing shot at the Galaxy Note.
Voice dictation will be a great feature for taking notes, writing quick iMessages, or playing Scriblenauts... and that's why it was included. I'm sure 70-90% of iPad users have iPhones so Siri seems kind of redundant in that regard for my reasons above.