A LinkedIn group for photographers hosted a discussion thread about Twitter and invited us to share our handle. But to do so, we had to agree to follow everyone else in the thread. My response:
Very sorry you make this auto-follow stipulation. I've been using twitter for 9 months and it's changed my life. I believe there are many completely legitimate reasons not to auto-follow someone back on Twitter.
Among the reasons not to auto-follow: curating one's own timeline for particular communities and posting-behavior/topics/usage level, frequency and style.
Twitter is very much about customizing your experience for your own needs.
Even the most 'expert' users are split on the idea of auto-following out of politeness/courtesy. I routinely check in to see what followers I am not following are tweeting, especially newcomers and infrequent posters, who may change their output and interest me. If my followers engage with me I often follow them back as I get to know them. however I choose to follow people on Twitter for reasons other than that they are following me.