Many employeers have specific requirements on the candidates. If you claim to be EJB guy but has never played on one of the above leading players of Application servers, who can trust you?
One exemption: Apache and Jakarta projects. They have strong industry momentum.
I am creating a small website for one of my friends using some open source stuff: Apache web server, Tomcat, MySQL. In addition, the OS is Linux.....However, if one wants to make his living in the IT industry, he/she needs to take a different appoach: embracing the products from ORACLE, IBM, MICROSOFT, BEA SYSTEM, RATIONAL SOFTWARE....