I like Joel's essays as much as anyone, but how is this not pure advertising?
To me this diminishes their credibility and puts me off their writing.
Strangely when I see Lessig doing this for his various causes it does not inspire the same reaction in me. Possibly this is because I don't think that Lessig is deliberately writing in a way that can lead directly to personal monetary profit, although he certainly could profit from his growing cachet due to his political activity.
Possibly I am just being cynical.