I have used this distro since their 10.0 release and have loved them ever since. It's great. They make using a GNU/Linux computer easy and fast to use. The distro doesn't play favourites between KDE and GNOME, the full CDs come with both. The drak tools are the simplest interface I've seen in a distro. Combined with their wiki and forum, help is always just a click away. As a commercial the are the only one who has made a public commitment to releasing all of their software under the GPL. The distro is so easy to use my Grandmother runs it.
Although I'm a more experienced user and now use Gentoo myself, I still think Mandriva is great for new GNU/Linux or new computer users. Most of the stuff works out of the box, including audio and video codecs. Mandriva Control Center makes it very easy to configure the system and manage packages. The new version 2007 Spring also makes it simple to enable all 3D desktop options (Aiglx, XGL, Metisse, Compiz). You can also buy a USB key with Mandriva preinstalled and this way your can take your desktop everywhere.