Someone was asking the other day how CS6 handled AVCHD. I haven't had a chance to try and yet but today I had to cut a job off an external USB drive (one of those little 'passport' numbers) and it was all fine, right from the copied cards.
I think the footage came off a FS100. It was mixed in a AVCHD MTS 1080 25p timeline with some smaller frame mp4s with no problem. All played in real time, even with rate adjustments. The only way I knew any different from anything else Ive been cutting is it was a bit laggy to start playing backwards on the timeline.
There is a bit of time when you first ingest the material where it generates peak files and stuff, but it's WAY quicker than transcoding, and still stable.