How will we make the suggestions? If you've logged in to YouTube and sent a video to a friend's email address, or if you have your YouTube account linked to a Gmail account, we will use this information to help identify your friends who already have YouTube channels. You'll only see channels whose owners have allowed themselves to be found by others who have their email address.
Want to see if you've previously allowed your channel to be found by others who have your email address, or want to change your settings? Just log in and visit the "Privacy" section of My Account. Look for the checkbox at the top that says "Let others find my channel on YouTube if they have my email address."