Reading the article “Mepis to switch from Ubuntu to Debian” one thing jumped out at me:
Woodford explained that Ubuntu is rebuilt almost from scratch every six months using source packages from Debian EXPERIMENTAL.
In using Ubuntu for almost 3 years, that was my experience as well. I formatted and installed fresh more than I just did a apt-get dist-upgrade.
And that is one of the major features of Conary – managing your applications and dependencies so you should never have to “install fresh”. Foresight, using Conary, believes in rolling releases – not big releases every 6 months, but incremental updates to keep you up to date with the latest software and security fixes.