I’ve been on twitter as @brammers for quite a few years now. It’s one of those few social networks I’m happy to be part of, as can follow the latest news in F1, the IT world and my other interests. Also it’s great for sharing snippets of information, and also good for a few small rants. 
I’ve also got a growing list of followers, who I will give my thanks for following me. I do sometimes follow back, but I have no fast and hard rules on who I follow back.
However here is a list of types of tweeters who don’t get a follow back. I also report them as spam, and they get blocked.
1. Obvious twitter spam. Yes those just @ replying with just a link, and nothing else.
2. SEO tweeters. In my eyes, you are just as bad as spammers.
3. Search Engine Optimisers. See 2 above.
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Keep your spam out!
P.S. I’ve hi-jacked that bit.ly link!