YouTube, MySpace and Real Time Content Filtering

In my weekly reading I ran across this article by Pete Tenereillo. It's a very good article overall but I do have something else to add. He suggests that blocking YouTube and other video sites at the firewall would be a bit militaristic. I see his point but in the past I have been known to take such actions. My reasoning was two fold. (1)It was against policy and (2) it was more cost effective to block those sites then invest in a content management solution. Now days the systems/solutions are becoming more cost effective and there is one company that is doing just what he proposes. I have not investigated cost or effectiveness and I would like to see a real world false positive statistic. Either way if it's against policy it should be blocked not mitigated.