Interesting. There are of course several people who doubt the actual recusal of the board from the deal, but when you look at this from a pure Facebook perspective, and not a board member perspective, it does make immense sense to purchase Instagram.
Instagram is pretty much the perfect way to take pictures and share them, so FB picking them up for $1b is actually akin to Google's purchase of YouTube. The notion that Zuckerberg did not consult the board is very logical as well - he knows the scrutiny they are all under, and such a critical deal getting substantively tainted by conflicts of interest would cause many issues in the long run.
The drum beat of "Instagram scam" posts and commentary about the conflicts of interest would be far worse if the deal were known well ahead of time. Zuckerberg is no fool and I'd expect him to be truthful in saying that the board had no knowledge - it is to their direct advantage to do so.