I also upgraded my project this morning, with less than 10 lines of code changes to switch the plug from 2.5.6 to 3.0.0 - the compilation errors were some casting issues of generics type - yes, Spring 3 is now compile-time type safe. If you use Maven, you may want to read about the pom and repository configurations here.
Second-and-thirdly, below are some notes I wrote down in company's intranet. :)
Spring Resolves Dependencies and Initializes Accordingly, Not You
Before that, I thought implementing the Ordered interface could impact the order of which beans shall first be loaded. Then I realized, it doesn't work. Ordered is used.. as far as I can tell right now, two on top of my head: during invocation of Bean and BeanFactory post processing and the order of Advices - just not Bean initialization!
So how does it really work (for which bean to be loaded before any other)? One thing that I found (or maybe really just one): dependencies - bean references and @DependsOn/depends-on. When the BeanFactory preinstantiates the beans, it resolves its dependencies (via BeanDefinitionValueResolver) and eventually the beans who are referenced/dependent by others will be initialized first.
Do take note that, you rarely use @DependsOn unless you have static (*ugh!!*) references. For my case, HibernateSessionFactoryBean depends on SubEntityManager and those enums in it are accessed via the static (*ugh!!*) method SubEntityManager.getInstance() by the SubEntityUserType.
Spring Shutdown Hook and Unit Testing
A Spring ApplicationContext has a close() method, things like HibernateSessionFactoryBean will only be destroyed when the context is destroyed via the close() method - which is triggered by shutdown hook. See AbstractApplicationContext.registerShutdownHook(). So what is important here to know is, if you are running unit tests, a series of them, destroy can only happen when the shutdown hook is called.
Here's an example, I was running two test fixtures but the first one didn't shutdown until the whole test execution exited.
[12-16 16:26:45] INFO GenericApplicationContext [Thread-4]: Closing org.springframework.context.support.GenericApplicationContext@1923ca5: ...startup date [Wed Dec 16 16:26:42 MYT 2009]; root of context hierarchy [12-16 16:26:45] INFO GenericApplicationContext [Thread-3]: Closing org.springframework.context.support.GenericApplicationContext@19b5217: ...startup date [Wed Dec 16 16:26:34 MYT 2009]; root of context hierarchy [12-16 16:26:45] INFO HibernateSessionFactoryBean [Thread-4]: Closing Hibernate SessionFactory [12-16 16:26:45] INFO HibernateSessionFactoryBean [Thread-3]: Closing Hibernate SessionFactory