What I've noticed:
- (usually) level intonation on "I know" with rising "intonation on "right" (for those who haven't heard it). Though sometimes I've heard it with just level intonation, kind of like an exclamation.
- often shortened to "right?" The diphthong is elongated as well.
- acronym IKR is used online and in text messaging
I associate this with teens and people in their 20s. Though I'm 30 and this has crept into my speech (since my classmates use it all the time). My friend from back in the boondocks recently told me that there's this "new saying" that annoys her, and I laughed when she told me it was this one.
While it seems fairly recent to me, Urban Dictionary does have an entry for it in 2003. But I do not recall hearing it then. Another Urban Dictionary entry (there are two!) suggests it originated in Northern California and another states that it's gaining popularity in Atlanta.
I'm interested in more metalinguistic commentary about this, particularly from those of you in the community. Basically, whether or not it's used where you live, the primary ages/gender/ethnicity/social class/whatever of people who use it, and how long you've noticed it. I'm interested in knowing if people in other English-speaking countries used it. I've noticed it used online by people living in the Philippines, for example.
What kinda motivated me is the Green Lantern Trailer. Where the Green Lantered (played by Ryan Reynolds) says it after he changed into costume. The video is in the cut and the relevant part starts at 2:07.