Here's something that some tweeters still don't understand. An @ reply and an @ mention are different things. A reply is directly to the person, and a mention is a tweet with the persons twitter name in it. Below are examples:
Tweet-
@amberlynnegirl is the bees' knees!
Who sees it?-
Only amberlynnegirl and your followers who also follow her already
Tweet-
Woo, @amberlynnegirl is the bee's knees!
Who sees it?-
All of your followers and amberlynnegirl
So this is why it's important to format your tweets with a character before the @name if you're promoting a tweeter (like for #followfriday, which is a hash tag / trending topic and a whole other explanation) and want to maximize the amount of people who see your tweet. Even a simple . before will work! (.@amberlynne girl is the bee's knees... follow her!)
All of the above will show up on your twitter profile page, but timelines are where tweeters get updates throughout the day.