Everyone knows that nice feeling in their gut when they see first follower in twitter account that they do not know. The first impulse is to show curtsey and follow the follower back and see account grow forth. This is especially true for people whose twitter account is part of their growing business. However, should you follow everyone back?
There are lots of opinions about that. I kind of like post in DoshDosh that you should not follow everyone: there are lots of bot users that use bots to grow their user numbers without any interest in you. However, your real follower policy should depend on your business model. So reasoning behind post about why it is useful to follow small guy is important too.
However, there are always people whom you can un-follow without any risk losing customer or useful connection:
1) People that follow lots of people and have no posts on their own. Usually there are very few people following them back. Later these accounts will spam you with ads, or they are trying to promote their blog that way (that is category 3 
).
2) People which all posts are made through tweetfeed – they just stream their blog, and you will not get any more information from twitter than subscribing through RSS. Remember, RSS is much easier for following posts than twitter. There are valid uses for feeding information in twitter: news bots, service announcements, etc. There is no need for them to follow anyone except for self promotion.
3) People whose all posts are adverts, bot messages and are not interesting for you. Believe me, they are here to sell you product and will not help you in any way. Sure, you can follow them if you are interested in their products, but do not expect any interesting discussion or help from their side. Sure, many people will drop an ad or 2 in their conversations, or promote their brand in other way. That is OK, as long as I get some information or at least their opinion free.
That is the policy I am using for myself in twitter. It works for me as of now.
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I do use Twitter with a commercial imperative, I have an eBook we’re about to launch, and obviously Twitter provides a valuable way of reaching an audience. However, it’s not the only marketing strategy, and we view Twitter as a long term activity, building up a profile around my area of expertise and interest.
To be honest after a few months of using twitter extensively I got bored and stopped. i rarely saw much benefit from it and most of the people following me seemend intent on trying to sell me things