Before I read this I noticed the revision had changed on SO from the SVN revision to 2010.4.23.1. Just switched to Mercurial from SVN myself and hit this same problem. We used to display the SVN revision on the site, but now that we have no true central repository, displaying a number that can be tied back to the source control system is a challenge.
How is the reverse date format for the site revision managed and then tied back to source?