EJB 3.0 are part of the majority of the mainstream application servers. Although EJB 3.0 are already very effient, lean and can be hardly further simplified - this is actually not the issue. You can save more and more money in the maintenance phase of an application. Although the economy tends to move in the direction of opensource application servers, serious applications always run on officially supported (opensource) application servers.
No one dares, mostly because of political reasons, to run critical software on unsupported platforms, regardles how good the own IT-department really is. ...and you have to spend some money on it. In general you get the support for EJBs included - it comes "out of the box". If you, on the other hand, deploying frameworks like Guice, Hivemind, Nanocontainer, Spring or even Seam (not on JBoss), you will have to think about the support for those frameworks as well. Such a mix is always challenging - at least the reproduction for a support case. In long term the cheapest possible solution will be the use of plain Java EE 5 containers, or a full stack alternatives like e.g. a transactional OSGI container or SpringSource dmServer. Running a full Java EE stack and an alternative on one box is just too expensive to be officially supported...
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