I recently started using Twittman.com and have had a decent amount of success - it makes you follow 100 twitter users per day, and all of these users are ones who have agreed to follow back whoever follows them. It has gotten me a decent amount of followers, but not many in my niches (very few clickthroughs for my tweeted links) - have you had any success with tools like this? Or should I be focusing on more a targeted audience?
Lots of these tools do just that, gather untargeted followers. Building your list manually is usually best or use software that will follow users from search results