Seriously though, the hours spent fighting dependency injection and Hibernate issues alone, when working on a really big Java project, could've been a full-time job.

For maximum fun, I once worked on a large ERP system that started out as a Struts 2/Hibernate 3/Jetty project and had an entire Rails app bolted on using JRuby. Some of the stuff in the JRuby side was injected thru Spring. ActiveRecord had to talk through Hibernate.