In the press release sent out by The Document Foundation, the team details why the fork was deemed necessary. The main focus seems to be to free OpenOffice from the oversight of any single commercial, and to turn it into a true community project. They don't say it explicitly, but the rather uncomfortable position Oracle takes towards Free/open source software certainly plays a role in this.
"We believe that the Foundation is a key step for the evolution of the free office suite, as it liberates the development of the code and the evolution of the project from the constraints represented by the commercial interests of a single company," states Sophie Gautier, long-time OpenOffice community member and former maintainer of the French language project, "Free software advocates around the world have the extraordinary opportunity of joining the group of founding members today, to write a completely new chapter in the history of FLOSS."
The Document Foundation and LibreOffice can already count on pretty much the entire Free software ecosystem, with all the major players pledging support; the Free Software Foundation, Google, Novell, Red Hat, Canonical, the OSI, the GNOME Foundation, NeoOffice, Credativ, NeoOffice, and others. Oracle has also been invited to support The Document Foundation, for instance by donating the OpenOffice brand.
Much of the early work will focus on polishing the code and lots of clean-up work, but in the future we can expect a more responsive and hopefully a more productive development cycle. One of the most important changes is the removal of Sun's requirement that copyright be assigned to them, which acted as a barrier to participation.
For now, major distributions such as Debian, Ubuntu, Fedora, and SUSE will ship LibreOffice instead of OpenOffice, and a beta release has been made available which at this point obviously doesn't differ much from the regular OpenOffice build.