Firstly, there is great value in these free technologies. Blogging, podcasting and social networking are great free forms of self expression, communicating and networking for people. People are out there sharing information and knowledge every second of the day. This has the dual benefit of serving as a form of expression for those who produce the content, and a source of information, interaction and advice for those who consume the content.
Secondly, companies gain the benefit of having content created for their sites, and the ability to track consumer trends by hosting these services, plus they sell advertising space. The gain for the consumer here, if you are comfortable with it, is this targeted advertising. Advertisers are able to save money, targeting their messages to people who match their specific criteria. That means that if you have to see ads, at least there is a greater chance that they will be relevant to you.