Writers on Twitter: Something's Not Right Here

So I signed up for Twitter in January, and have been making efforts to follow writers, publishers, self-publishers, and anyone connected with the biz. It's been less than a month, but I'm already seeing two distinct camps in terms of the kind of content writers on Twitter are putting out:

(a) Rampant self-promotion, as in the following: 

• Review for MY BOOK: "Amazing, best book ever, love love love, buy buy buy" #tag #tag #tag
• "Your life will suck unless you read this book" MY BOOK TITLE HERE amzn.link.buy.my.book
• "TITLE IN ALL CAPS HERE" ORDER YOUR COPY TODAY!! PLEASE RT!! #TAG

 (b) Helpful or interesting articles about writing, contests, etc.: 

• Twitter writing contest!  Enter here: bit.ly.link.to.something.useful
• Neil Postman Award: The author of the chosen poem will receive $500
• What (TV Show name) Can Teach Us About Creating Character Archetypes

I scan tweets every hour or so, and it seems that at least 60% of them are shoving someone's miraculous one-of-a-kind book down my throat.  Guess what?  I saw that tweet the first time.  And the second.  And the third.  I know your book was reviewed by Kirkus.  Hell, I can probably quote the review verbatim by now.  Does it mean I'm going to buy the book?  No.  It means I'm going to unfollow you because all you can add to my day is the umpteenth all-caps mention of your book title.   

Do these people ever get tired of pasting the same messages into HootSuite or SocialOomph? Does this kind of guerilla marketing actually work?  

If these writers are selling books and making money, more power to them.  It just seems like the point of screaming into the ether is to have something to say.  "GIVE ME YOUR MONEY" isn't really the message I want to be remembered for.