Sun Microsystems claims that iPlanet application server is the number 1 application server. Read the article:
http://industry.java.sun.com/javanews/stories/story2/0,1072,33304,00.html A comparisation table can be found for a wide range of application servers at
http://www.flashline.com/components/appservermatrix.jsp The following are my personal comments:
Also, iPlanet application server is the most expensive application server. Industry has a shortage of iPlanet developers. Many companies likes to use iPlanet server. But since they cannot find skilled people they use alternative application servers like Weblogic or WebSphere. Be one of the people to sell yourself in such a disasterous job market. There is certification for iPlanet app server. This may give you something to start with.
This is what I have seen when I was working on a six-million+ dollar e-commerce project using iPlanet app server. We hardly found any good iPlanet people in Australia for the project. But, the things we wanted to do other app servers could not do them. So, we had a hard time.
Faisal