Currently, there is not officiel changelog. But you can read the bazaar log, by using this command (under linux) or Tortoise Bazaar GUI (on windows).

bzr qlog lp:openobject-server

This will open a window where you will se the recent commits. Of course, you might have to do this for different repositories : lp:openobject-addons (addons), lp:openerp-web (web).

great, thank you , am using tortoise on widows. 2 questions: where can i find all repositories. how do I know which commits have been added to the nightly? or everything is added?