As a disclaimer, I am a newbie to video editing. I bought a Sony SR11 about 3 months ago have just started reading/playing around with this, so take whatever I say with a grain of salt.
From what I understand, importing to iMovie converts the AVCHD to Apple's own format and increases the file size. Instead, I was able to copy the .mts file directly from the camcorder's hard drive (linked to the iMac via USB) into Toast (after the $20 blu-ray upgrade). Then I burned a blu-ray formatted disc on a regular DVD-R in my iMac's superdrive. This will not play on a regular dvd player (since it is blu-ray formatted and high def), but it does play on my PS3 and Panasonic BD-30 without problems. I can't notice any difference compared to hooking the camera directly.
I just got a blu-ray burner and haven't tried that yet, but it should work as well.
Note: This is just raw footage from the camera without editing.