The problem is the format (AVCHD) is not supported by OSX -- While you can import it into iMovie you can't import it into iPHoto and it doesn't show up in quiclook.
I haven't (yet) fixed the iPhoto problem but I did go about fixing the quiclook plugin.
This little plugin should be installed in your ~/Library/QuickLook folder (create it if doesn't exist) and it should give you both thumbnail previews (the first frame) as well as a video preview (It may not show the whole video if it's long as quicklook only gives about 30 seconds to generate the preview)
Source code can be found here https://github.com/loghound/AVCHD-Quick-Look
I can't offer any support but you can grab it here