I also haven't used Yellow Dog in a long time. My distros of choice have been ubuntu and gentoo. IIRC, Yellow Dog was based off of a Red Hat distro, so it would be advantageous to use it if you wanted to learn how RPMs (and YUM) work, or just how Red Hat does things. I personally think that Ubuntu is a really good distro, and if you're happy, there is no reason to switch, unless you want to learn something else...