I recently built an AMD 64-bit dual core machine, and installed Ubuntu Edgy for x86-64 on it.  One thing I found (and had read elsewhere) is that 64-bit Eclipse is buggy.  It hangs and dies usually within 30 minutes, and sometimes on a few minutes.  And I found the performance improvements to be hardly noticable, so not worth the hassle of frequent crashes.

My solution was to switch back to the 32 bit Eclipse.  Not hard, but not dirt simple.  First install the 32-bit JVM ia32-sun-java5-bin.

sudo apt-get install ia32-sun-java5-bin

At this point, you may find that the 32-bit JVM is set as your default JVM.  Not what we necessarily want to do.  Fix it thus:

 sudo update-alternatives --config java

Then choose your 64-bit JVM as the default.

Now, download the 32-bit Eclipse.  You can extract it anywhere.  I put it in my home folder under ~/Applications/eclipse32.  But, here's the problem: it won't run due to ELFCLASS32 issues because you have the 64-bit JVM on the path.  If you are like me, you try setting JAVA_HOME to point at the 32-bit JVM.  But that won't work either.  Eclipse doesn't care about JAVA_HOME.  It depends solely on finding "java" on the path.  The solution, for me, was to write a bash script called "eclipse.sh" in the eclipse32 folder as such:

 #!/bin/bash
PATH=/usr/lib/jvm/ia32-java-1.5.0-sun/bin:$PATH
/home/username/Applications/eclipse32/eclipse

You'll of course need to change the path to the eclipse binary.  Then, you need to set the executable permission:

 chmod +x eclipse.sh

Now, you should be able to run eclipse.sh and get 32-bit Eclipse, and the crashes and hangs will be a thing of the past.