iPhoto 9.3 does not seem to import AVCHD 1080p; only 1080i and 720p.
Anyone interested in importing AVCHD into iPhoto 9.3 needs to be aware that iPhoto 9.3 seems to support only AVCHD Lite (720p) and AVCHD (1080i). It does not seem to support AVCHD Progressive (1080p); it does not even show it in the list of camera files to import from. Attempts to manually copy folders from the camera memory result in lots of messages about unsupported file formats, similar to the ones Apple say you will get if you do not exactly follow their instructions for which folder(s) to copy.
In my camera, a Panasonic FZ150, after choosing AVCHD for REC MODE, the user can choose from three setting for REC QUALITY, which are: PSH" (1080p), FSH (1080i) and SH (720p), all at 60 fps. Other recent cameras supporting AVCHD should have similar choices, so if AVCHD import to iPhoto is not working for you, I suggest you check which form of AVCHD you are using.
Apple was vague about this in their description at
http://support.apple.com/kb/HT5251, and just said AVCHD.
Unless this is a problem unique to my camera and/or iPhoto library, Apple should have said: "AVCHD Lite and AVCHD only; not AVCHD Progressive." (And probably not AVCHD 3D either!)
I asked Apple today (19 June 2012) to clarify this in their website, in iPhoto, and in all documents describing iPhoto.