Marc Andreessen sells nearly half his Facebook stake
marketwatch.com
marketwatch.com
The point I'm trying to make is that buying and selling stocks usually says more about the investors rate of return goals and less about their opinion of the underlying company.
"These plans are widely used by officers and directors of public companies to sell stock according to the parameters of the affirmative defense to illegal insider trading available under Rule 10b5-1, which was adopted by the SEC in 2000."
http://corpgov.law.harvard.edu/2013/02/05/rule-10b5-1-plans-...
A perfectly legit 10b5-1 which would have resulted in exactly what we saw here. In February Barron's reported Andreesen's sales as being directed by a 10b5-1 plan: http://www.barrons.com/articles/SB51367578116875004693704580... so he's clearly familar with the process.
You can see a list of Insider Trades here: http://finviz.com/quote.ashx?t=FB
In the same time period he bought 50,145 shares of HP (on 11/2).