Blastfollow blessing or spammers dream

BlastFollow enables you to follow Twitter users who share your interests
en masse. This is accomplished by searching for users who have
tweeted with a particular hashtag recently. For example, if you are
interested in event , you may want to search for users whose
tweets
have included the hashtags for example #event or #interest.

now this is great for conference type events or those following specific topics but also might be used to collect user accounts by spammer . You decide I quite like it

http://blastfollow.com/