I am mainly interested in the 'integration features' between the IDE and the application server.
One example would be GUI editors for various server specific deployment descriptors.
Another example, from the NetBeans IDE integration with GlassFish, is the ability to:
- edit a java file that is part of a web application,
- save the file and
- see the effect of the change that you just saved in the browser (without a bunch of reloading).
Please include a link to any reference to the feature in user docs, if you have it at the tips of your fingers.