I just upgraded my workstation to Hardy and got a SIGSEGV when starting Eclipse.  It appears to be a bug in the Sun JVM that ships with Hardy, and it only happens on AMD64.

If you're set on using this runtime, the fix is to disable the JIT compiler by launching Eclipse with -Xint, but that's comes with a severe performance penalty.

The fix I used was to simply downgrade the Hardy JRE (6-06-0ubuntu1) to the Gutsy version (6-03-0ubuntu2).  You'll have to edit /etc/apt/sources.list to add a Gutsy repository.

I'm pretty sure this is the Sun bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6614100

And this is the Ubuntu bug: https://bugs.launchpad.net/ubuntu/+source/eclipse/+bug/174759