The version 0.6 of symfony is still in alpha state, and it's being tested and tested so that you have no problems when migrating your projects. It will soon be released in a stable version.
In the meantime, if you are curious about the reason why we decided to break backward compatibility, check out this detailed description of the new features of the 0.6.
If it doesn't convince you to switch to 0.6 right now, we hope that it will comfort you in your griefs against the few manual manipulations necessary for the upgrade...