Attached is my rough attempt at a script to auto-generate Misc/NEWS from commit logs. Key points:

- Works from the hg log in XML format as dumped to a file
- Considers a commit newsworthy if it isn't a merge and either has an issue number or has an "interesting" path (e.g. not an HTML file) and details (i.e. the stuff after a \n\n)
- Uses paths in the commit to determine what category the commit belongs to

Decisions to make:

- How to exactly flag a commit should not be in NEWS (I say it doesn't contain "#\d+:" to signify an issue and lacks any details after a \n\n)
- How often to run (e.g. at release time, anyone, post-commit hook, etc.)