I recently compared the installation of Mageia3 with Fedora 18 (both done in a VirtualBox virtual machine). When installed and fully configured to taste, you have essentially the same level of usability and ease of administration with a similar choice of desktop environments and current versions of applications running on a recent kernel using SysV-style init and RPM packaging. The meaningful differences are more easily illustrated with some history, so this will not be the typical, dull, useless version-to-version comparison with a plethora of gratuitous screenshots and the inevitable inane jargon overload.
Fedora has been the community release of Red Hat since RHEL became the primary distro for Red Hat proper. It enjoys a more frequent release schedule than RHEL and is more focused on the desktop. Think of it as the development version of the workstation companion to the Enterprise version of Red Hat Linux taht is now in its 18th release.
Mageia would seem to be a relative newcomer, only now in the beta of its third release, but its roots go back to Red Hat 5.x with the release of Mandrake 5.2. Mandrake was essentially a re-spin of Red Hat with better default configurations and an emphasis on the KDE desktop (RedHat has long been GNOME-centric). A great idea plagued with poor corporate leadership and even poorer corporate decision-making, Mandrake-come-Mandriva focused its development in three areas: its package manager, its administration tools and its volunteer community. Red Hat at the time still relied heavily on a text-based installer, RPM and linuxconf, all of which required more than a modicum of command-line mojo. RedHat were just beginning to develop admin tools written in Python.
The Perl programming language was adopted by Mandrake, both because the initial cadre of developers were proficient in it and also as a way to differentiate themselves from Red Hat. As well, they would not be simply "improving" admin tools over which they did not have final control of the source code. It was a bold gamble that both benefited them and undermined their success as few other distros have adopted their tools.
Red Hat through the years only begrudgingly accommodated their non-corporate user base and actively undermined them at times. For example, Red Hat's early incarnation of KDE was so heavily edited to make it less configurable and more GNOME-like (and better suited for a corporate workstation) that it elicited an uproar from KDE fans while documenting the Red Hat developer's overwhelmingly "not invented here" mentality (as evidenced by their scurrilous code comments). Fedora/Red Hat has always been a GNOME-centric distro because the limited configuration options of GNOME provide the best fit with their corporate workstation focus and because many GNOME developers work for Red Hat. Red Hat, in the name of "free software" also made their distro very multimedia unfriendly by not only not providing easy access to integrating less-than-free multimedia software, but by not compiling in support for them if you wished to add them on your own. Again, it was a more corporate-centric, IP attorney-friendly approach.
Many of the Red Hat/Fedora usability advances in package management and desktop ease-of-use were fomented by the loyal non-corporate user base. But this made the installation and configuration of a usable home desktop system and easily updatable system a nightmare of tedium, spawning alternatives like Mandrake and KRUD, Kevin's RedHat Uber Distribution, which provided a more friendly configuration and a way to deal with updates that addressed "Dependency Hell"; it was made obsolete by the eventual adoption of YUM as the RPM wrapper and the growth of the Fedora user community.
The Mandrake/Mandriva installer was steadily improving but idiotic corporate decisions were killing the distro: non-sensical acquisitions and pursuit of computer-aided training pillaged the start-up capital, but the user community was strong. Meanwhile, the RPM wrapper application URPMI and the user/administrator tools were coming along and Mandriva offered the broadest out-of-the-box hardware compatibility of any distro. Complicated configuration of things like X11, sound and printing were almost fiddle-free and automatic. However, Mandriva's choice of desktop and system graphics was uninspiring and almost child-like, certainly not as cutting-edge and sexy as the up and coming Ubuntu.
Red Hat spun off the community version of Red Hat as Fedora Core, then as Fedora. A growing user-focused community sprang up to address it's usability shortcomings and has flourished. Mandriva corporate neglected its user community and as it approached bankruptcy for the second time, abandoned the desktop version of Mandriva to community users and departing employees under the auspices of Mageia.
The official Mageia base install continues to demonstrate the ease-of-use "just works", broad hardware support, sane default configurations and a community-focused multimedia desktop. The official Fedora base install continues to demonstrate the corporate-focused minimalist approach Red Hat has traditionally taken to support their Enterprise version and, as always, a strong community effort continues to take up the slack and make it usable as a consumer desktop.
Desktop-focused Mageia has finally stepped up its default look and feel to a polished, sophisticated and modern level while corporate-focused Fedora looks flat and clunky in comparison (still, Mageia could use some more sex appeal). The bottom line is a very different out-of-the-box experience. Mageia's installation, default configuration and usability all best Fedora. Still, you can wind up with a very usable and essentially similar consumer desktop experience using either distro; Mageia just gets you there with less work and fuss. Overall, Mageia appears to have found it's raison d'être.