Did an upgrade cycle from 10.04 through 11.10, installing every release. Did a clean install at 12.04. Have upgraded that to 12.10 and now 13.04. I will not say there were no issues, but I never faced data corruption or unable-to-boot issues during this time. What I did face though was random errors and broken packages. But I did not document those erors, so I cannot go into any specifics.