When you are configuring unstable branch of Inkscape, do this with sth like "configure --prefix=/opt/inkscape" or "configure --prefix=/usr/local", this way you will be able to keep SVN version of Inkscape next to stable one from repository.
I'm currently using those packages on Debian:
http://art.sidux.com/I can't guarantee you that they will work under Ubuntu, but some time ago I was using Inkscape packages for Ubuntu under Debian and they worked fine.
Also try moving your ~/.inkscape dir away, sometimes some specific settigns cause segfaults (if you have merged svn version today, Inkscape already uses blank config from ~/.local/Inkscape).