Ok, my shush account concept is causing a bit of confusion with some folks so here's some common answers.

1) a "shush" account is just a normal Twitter account. It doesn't tweet and serves solely as a topic placeholder. Why? See 2)

2) If you decide to tweet about (say) Blackberry mobile phones (and you don't think it is relevant to your regular followers) then you can prefix such tweets with the @shBBerry account (i.e. a Twitter reply)

3) Because of how Twitter replies work, only your followers who additionally follow @shBBerry will see these tweets.

4) Therefore you probably want to let people know that you are using sushes like @shBBerry. For instance you can tweet it occassionally ("hey, I'm also using @shBBerry", you can put it in your bio, you can put it in your Twitter background (look at mine), you could give them an auto reply when someone follows telling them about which sushes you use (this is the only time I've come up with a good reason to use such a tool!)

5) I've only created shushes which are relevant to me (listed here). Please feel free to create more. Best to prefix them with sh (for "shush!")

Hopefully that sheds a little more light!

updated:

6) Why don't shush accounts tweet? Because they are only acting as topic placeholders. If they additionally tweeted then, when you prefixed your tweets with (say) @shBBerry, are you tweeting about a topic or replying to a tweet from @shBBerry? Therefore, to avoid confusion shushes do not tweet.