GA will tell you that, if you use it.
I've seen some really interesting mobile trends lately. Last year, my traffic was all about the iPhone. This year, Android is *far and away* the largest mobile platform - by like, 600% (and that's even after I filtered out my developer who has an Android phone, ork ork)
On the other hand, for one of my B2B ecommerce clients, their mobile traffic is still a small percentage in actual numbers, but is up some 300% over last year, and it's almost entirely iPads. Which makes sense, if you think about it.
Mobile accounted for 20% of my AdSense income since June 1 (of the people who view as mobile. I have iPads set to view the regular site, as it renders just fine and displays regular ads on iPads) That's well into four figures, and not inconsequential to me, so I will be continuing to pay close attention to mobile, that's for sure.
Can't post a link here (I don't think) but Mobile Moxie has a web tool where you can view URLs as different types of mobile devices and compare them, if you want to see how your site looks. I'm sure you all know how to Google it.