I just ran through a test of transferring the AVCHD files from my card to the computer and working with the MTS file. My question is; what are all the other files that get transferred. I'm assuming they're some sort of metadata. As a test I deleted everything but the MTS file and it still worked fine when importing to CS4.

Those files are data files that let programs like Final Cut Pro identify avchd files and somewhat automate the download and transcoding process it uses. Probably other NLE's as well; FCP will not find the files unless the entire folder and all subfolders are present. You may have software that handles the mts files directly. /Battle Vaughan/miamiherald.com video team