There was a short piece about this on the Today prog, including a brief interview with a not particularly talkative Carolyn Casady. Here's a little more:

http://www.boston.com/news/local/articles/2006/07/27/kerouacs_road_will_be_unrolled/

Apparently this includes passages about drug-taking and gay sex which the world wasn't ready for in the mid-50s, and uses the characters' real names rather than e.g. Alvah Goldbook ...

UPDATE: Amazon has publication dates of Aug 16th 2007 (US edition) and Sep 6th (UK).