For at least a year, I had used TweetSpinner as a free account, but recently I decided it was time to upgrade in order to get more relevant Twitter followers. I'm not really interested in having "the most" followers, etc., but I am interested in creating a list for my genealogy friends so I can get updates from their posts and tweets.
On August 8, 2010 I posted You May Have Been Pruned here on Pentimento, and it was soon after that I subscribed to the paid version of TweetSpinner. Rest easy, I'm still not an affiliate. But, I have noticed a gigantic difference in the amount of followers I have, as well as their content. It's been pretty easy because I set up keyword following for #genealogy, and mimic following for my friends like @footnotemaven @geneabloggers @dearmyrtle @familytreemag and @ancestrydotcom
When I have a new follower I'm able to automatically send a direct message (DM) that says, "Thanks for the follow! I hope my tweets keep you interested and involved."
One of the other features I love is that with one click of the mouse button I can de-spam my inbox, or prune my list of followers as mentioned above. One thing I would caution you to understand is that Twitter works with TweetSpinner and you can't do things too quickly on TS or Twitter won't like it.
I pay $14 per month for TweetSpinner, which I feel is a good investment. Have you used TweetSpinner? Are you thinking of using it for your Twitter account?