Have you signed up for a Twitter application or service, then discovered it posted to your Twitter feed without explicit permission? This is definitely bad Twitter behavior. Let the user evaluate your app/service and tweet to their followers, after they have deemed your app/service useful.
I’m naming this the “cheat tweet anti-pattern.”
Apps & Services using cheat tweet anti-pattern
http://twtlab.com/love – Suggests Twitter users you “love” and tweets automatically after you authorize access
Cheat tweet: “My favorite users are @user123 @user124 @user125 ! Perhaps this is love 
http://twtlab.com/love“