Why would I want to use java portlets above tomcat and gwt? Would portlets make it less- or un- necessary for me to use jsp and jsf? Has Jboss been part of the portlet evolution culture? Does Jboss satisfy the portlet jsrs?
What portlet implementation/brand would run on gae java and gae python? Are portlet specs due to peer pressure from php cms culture?
What are the equivalent of portlet and portlet jsr in .net?
Portlets were a well-meaning but mis-guided attempt at a reusable widget API for web applications. Think of the personalised google home page, with the portlets like weather, news, mail, etc.
Unfortunately, they made a bit of a mess of it. The Portlet API is a bit of a pig, a real barrel of not-fun, and there are very few implementations of it. The only one I've ever used is JBoss Portal, but it's a bit of a brute, and rather buggy. Liferay may also be a portlet server, but the home page is heavy on fluff and light on information, so I can't tell.
Spring provides an MVC framework for the portlet API which tries to reduce the pain, but frankly I wish they hadn't bothered, it just clutters up the documentation.
Essentially, the whole shebang looks like a solution in search of a problem.
If you happen to have a framework that you need to use, and it supports portlets, you may find then that portlets are going to be useful, since the application is built with the idea, but, as others have mentioned, if you are starting on a project, there are many other technologies that will do what you want with less effort, in a more stable environment.
For example, when I worked at the University of South Florida, the learning management system was (and is) Blackboard, and they now support portlets: http://www.ja-sig.org/wiki/display/JSG/Blackboard+Portlet. So, if the application provides an API, and expects people to use portlets, then it may make sense to look at them.
UPDATE:
After looking at the question there were a couple of things I missed.
Portlets were an attempt, it seems, to try to do as Google did on their homepage, where you could have multiple unrelated blocks of information on the webpage, so you could track your stack portfolio and your favorite hockey team, for example. I don't think it was influenced by PHP CMS as it was just an idea that was ready to come about, and if you need the server code to help pull the information, and to tie it into an application, this was one approach.
The closest thing in ASP.NET that I can think of to portlets are controls. I could have a stock portfolio control and when I include it on my page, you can set the options and it will show you your stocks and hockey team scores.
Not everyone uses JSF, for example, so controls would need to be written by hand as JSPs and servlets, with javascript.
Why would I want to use java portlets above tomcat and gwt?
These technologies are not directly comparable. Coming from regular web page development, Portlets seem like a very restrictive technology. But then the value of Portal servers is largely the control they give to administrators and users - the fact that this makes your life more difficult is irrelevant.
Would portlets make it less- or un- necessary for me to use jsp and jsf?
You can write directly to the output, just like you would in a Servlet. You probably still want a view technology (that will have to support portlets).