Hudson core still uses Subversion, and the java.net svn server is kind of slow. I needed to do some diffs when investigating a fix for an issue I encountered. I had to wait a couple of minutes for every single diff I wanted (from the log, not local diff).
I'm still a Git / Mercurial newbie... but it's obvious that if you're a remote user, centralized vs distributed source control isn't even a fair comparison. It's that much better.