Some of the bots could be beneficial if used correctly. Some of the promotion bots etc provide services in the way an advertising company like adwords or adsense would. You make a bid on an advertising spot, and the bot fulfills this. This service is not free, and is highly lukrative for those with the resources to start and manage them. I honestly don't see a problem with the bots unless their owners are distributing their tasks with hidden malicious agendas :P