There's a 3rd volume "The Performance of Open Source Applications" now, and it has a chapter on another high performance HTTP server, Warp:

http://www.aosabook.org/en/posa/warp.html

Interesting what kind of performance one can get out of GHC nowadays. Article says the authors of Warp had to implement a new parallel IO manager for GHC to get there, but that was merged into GHC 7.8.