Twitter has a wonderful system in place for @replies. If you start a tweet with @username, that user will see it. Anyone who is friends with both you and the user will also see it. Anyone who is not friends with both parties will not see it. This is good. Here is why.
Let’s say that you’re friends with both Han and Chewie. Han posts “@chewie Ha! She called you a walking carpet!” You will see this reply and get to laugh along with your buds.
Now let’s say that you are not friends with Leia. Leia tweets “@Han I love you.” and Han tweets “@leia I know.” You will not see either of tweets because you are not friends with Leia and probably don’t care.
Now let’s say you are Boba Fett and actually want to see who Han has been replying to because it may help you track him down. You can go to Han’s profile page (click on their name and then click “Tweets” or go directly to their page, i.e. www.twitter.com/han) and you will see ALL their tweets, including replies to anyone. And, when used correctly, you can click on a reply and it will expand and show you the original tweet as well so you can see what the reply is referencing! Awesome!
Now here’s the problem. Some people (all celebrities, in my experience), for some reason think, “Hmm, if I just @reply, then not all my followers will see that reply. Only the recipient and anyone who is friends with us both will see. I want to force it on EVERYONE!” So they tweet something like “.@han I want my money, Solo!” or “via @han That @greedo had it coming!” or they start their reply with an open quote before the @.
Since the tweet doesn’t start with the “@” symbol, it’s not treated like a reply, but like a normal tweet and all of your followers will see it. This also means that people can’t click on the reply to see the original tweet and thus will probably have no idea what your reply is talking about. This is annoying and spammy. Let me give you an example.
I used to follow a certain celebrity on Twitter. This person interacts with his fans a lot, which is awesome. However, instead of tweeting “@superfan Thanks! I’m glad you liked it!” which would mean that I would not see his reply since I do not follow @superfan, he tweets “via @superfan Thanks! I’m glad you liked it!” and since that doesn’t start with “@” it now appears in my Twitter stream. So as he sits there replying to tons of people, my Twitter stream is flooded with all his replies which I may or may not care about. If I want to see everything he tweets, I can go to his page and see all his witty interactions (and then click on them if I want to see the tweet he is replying to), however I would rather not have my Twitter stream spammed by all these replies that were forced upon me by bypassing the “@reply” mechanic. I ended up unfollowing this person because he rendered my stream virtually useless (he also likes to write long messages simply broken down into 140 character chunks, which I also think is a misuse of Twitter, but that’s another story).
So please, stop thinking you know better. The system is designed that way for a reason. If you are replying to a tweet, just hit the reply button or start the tweet with @username of the person you are replying to. Those who want to see all your replies can, and those that don’t won’t. If you abuse the system, then the people who don’t want to see those replies have no recourse other than to unfollow you.
Keep in mind that I am just talking about replies. There are also “mentions” where you are basically just tagging someone else like, “Hey, everyone, @luke lost his hand so send him well wishes.”