A few Defcons ago, Jason Scott gave an excellent talk about this failure mode[1]. Basically, companies host user-generated content for free. Then years later, they destroy it with little or even no notice. Sturgeon's law applies; most of the deleted content is crap. But a lot of it matters to the people who made it. More importantly, a small fraction of it is stuff that future historians would kill for. Collectively, companies that engage in this behavior are burning historical evidence.
I find it hard to get too wound up about an only copy that has been turned over to a third party. I get that the user understanding the situation well can be a problem, but it isn't a very careful thing to do.
1. Archive Team: A Distributed Preservation of Service Attack http://www.youtube.com/watch?v=-2ZTmuX3cog