If you are on a linux system, it is easy to do a debug backtrace, which provides very useful information about the crash to the developers:
in a terminal, type: gdb freecad (assuming package gdb is installed)
inside gdb, type run
after the crash, type bt to get the backtrace, that you can include in your bug report.
Guide for submitting reports: http://www.freecadweb.org/wiki/index.php?title=Tracker
"To do this, you need to be running a "debug build" of the software. "Debug build" is a parameter that is set at compile time, so you'll either need to compile FreeCAD yourself, or obtain a pre-compiled "debug" version."