I just picked up a new 2012 E91 on EU delivery back on May 30th.
I looked for used ones for quite a while, but found next to nothing. As a result, I decided to go new while I still could. A manual transmission was a must for me, so that made the search even harder. I ended up getting the M-Sport package too which offers the blacked-out trim and really nice sport seats.
I see a few E91s around the Seattle/Eastside area, but not many. I had the windows tinted at Accutint and the guy there said he'd never even seen one.
I like the car a lot, although it's definitely a different vehicle than my E46s and E36 M3. The only things I would criticize so far is the horsepower (the car would benefit greatly from another 30-50 HP) and the brittle, crappy feel and noisy ride of the runflats. The horsepower is hard to fix (cheaply, anyway), but the runflats go away next week, to be replaced with Pilot Sport A/S tires for the upcoming winter season. Aftermarket 18" BBS RS-GT wheels with Pilot Super Sports go on next summer.