You can edit AVCHD on a Mac using iMovie ’11 — after a fashion. This is from the Apple website:

“iMovie ’11 does not edit AVCHD video natively, it instead converts this to AIC (Apple Intermediary Codec).

“This does slow down the importing of video; however, the editing speed is much faster.

“Editing native AVCHD video can be performed by some video editing apps, but the rendering process is much slower.

“This is because AVCHD video records data differently – in order to save space, only pixels which change from one frame to the next are recorded as new frames.

“This enables AVCHD video to take up less space on memory cards and hard drives, but does slow down editing significantly, as the editing app needs to re-render each frame separately, with a full set of pixels per frame.”