Exoplanets: Will intelligence be common or rare?

In "Intelligence: A Rare Cosmic Commodity", John D. Ruley profiles the views of Professor Andrew Watson who argues in Astrobiology that intelligent life on the exoplanets (planets orbiting stars other than the sun) is likely to be rare. Watson, who studied under James Lovelock (of the Gaia hypothesis), estimates,

the overall probability that intelligent life will evolve as the product of the probabilities of each of the necessary steps. In his model, the probability of each evolutionary step occurring in any given epoch is 10 percent or less, so the total probability that intelligent life will emerge is quite low (less than 0.01 percent over 4 billion years). Even if intelligent life eventually emerges, the model suggests its persistence will be relatively short by comparison to the lifespan of the planet on which it developed.

Given that we only know about life or intelligent life right here where we live just now, I think some of this would be better as fiction than non-fiction, but it is interesting to hear about anyway.