Something clicked recently, after I compared a couple of scenarios of recently life.
The two cases have to do with extending your framework, especially on the bleeding edge.
Extending Java: Hibernate and XDoclet
To get things working, both Hibernate 3, and the XDoclet 2 plugin had to be patched, resulting in our own builds.
Luckily, there are JIRA issues filed, and in the Hibernate 3 case a fix seems to have already been put in.
Extending Ruby: Rails
In another life, a Rails project needed to alter the way Rails did something. Rather than having to have a special jar file, or dependency, or anything like that, all that needed to be done was to re-open the classes that needed tweaking, and change the methods!
Having a system that allows open classes is a pleasure when it comes to making changes like this. So much cleaner!