“Java 5 added a number of powerful language features: generics, enumerations, annotations, autoboxing, and the enhanced for loop. However, many shops are still tied to JDK 1.4 or earlier and may be for some time to come. But it’s still be possible for those developers to take advantage of these powerful language features while continuing to deploy on earlier JVMs. Brian Goetz returns from his hiatus in this installment of Java theory and practice to demonstrate how.”
The reason why most of us are stuck with 1.4 is because of app server vendor support. Even though most of the vendors now support a 1.5 complaint version of their app server, many companies are still running older versions.
In many cases these are mid to large side companies that rely on support from their vendor. I can think of you would have better success trying to convince them to upgrade to the latest apps server that supports 1.5 features then you would convincing them to use retrotranslator or retroweaver.
Only place I can see people using a technology like this is framework developers, and other companies that supply libraries that they certify and support as being 1.4 compatible, but still want/need to take advantage of 1.5 features.