One of the things that search engines look at when they are working out whether a site is likely to hold spam content is the neighbourhood your site is in. Who do you link to, and who links to you. In social one could see how this was important, Twitter are using those signals to provide follow recommendations to on Twitter. Which means that the organic growth of your Twitter account is at least partly attributable to the quality of the existing followers.
Buying followers looks even less attractive than it has done previously. When looking at setting KPIs based around Twitter followers look less at the number of followers and more at the quality of them as this will provide organic growth in its own right over time.
New tailored suggestions for you to follow on Twitter – Twitter Blog
Archived from the blog that I used to write for PR Week.