Enjoyed it a lot. I found it very informative as far as giving a lot of actual real information about the history of computers and codes... it inspired me to look up some facts to double-check things! Not really SF, per se, but definitely for those interested in sf/cyberpunk, as well as historical fiction.
Typical Neal Stephenson story - lots of interesting characters, plot twists, and a touch of technology. I read everything of his that I can get my hands on.