The versioning scheme is 8.0.YMMDD.NN and that explains 8.0.50727. The mystery is with the build number .42. There are three top contenders for it, and no prize of guessing the correct one

1. People were so impressed with my blog that they borrowed the number from my blog title
2. Visual Studio 2005 is the answer to the universe. For people who have not read Douglas Adam's, The Hitch-Hikers Guide to the Galaxy, buy a copy and read it.
3. When we come close to the ship date we freeze everything else other than the dot build number, which gets incremented each time a new build is churned out. Incidentally the forty second build was the good bits that got shipped.