Steam recently changed the default privacy settings for all users. This may impact tracking. Ensure your profile has the correct settings by following the guide on our forums.
I had this same problem when installing Windows 7 before. I wasn't able to find a fix for the problem though :(
Thankfully I had a time machine backup, so i just reinstalled OS X and got all my files back :D
The easiest way to download youtube videos on mac imo is to use the activity menu within safari. Go to Window > Activity and it will bring up the menu. Look for the largest file in the list because that is the video. Just double click it and it will download it. Then convert the .flv to .mov or...