I agree with Manuel, the internet wouldn't exist without open source contributions. The problem is, big business will always take an interest in anything that manages to generate attention passively. A product or service that can reach customers with little or no advertising spend has to be appealing for reasons other than their social good.
In most cases, it all comes down to how much big business can squeeze out of a service before it falls out of favour with it's users.
Consider MySpace. As far as I can see, it's main source of revenue has always been through advertising. It has been clever in the ways in which it generates this advertising revenue (leveraging targetted music, promotions etc..) but I think it'll be interesting to see how the service changes as MySpace's new owners decide it's time they saw some return on their investment. Surely they're not expecting to see enough return through advertising revenue to justify the purchase cost?
As soon as big business gets involved and return on investment becomes the priority, the initial idea behind these services will become obscured behind quarterly balance sheets.