What frameworks are people using to build java Portlets – in particular the user interface part?

I know the EXO people use JavaServerFaces, and I think both EXO and Liferay come with Stuts bridges. I'd love to hear peoples impressions of how well that work.

I believe Struts 1.2 adds (some?) support for Portlets, but I'm not sure how far it extends.

I've been using the Portlet support in the Spring sandbox with some success, but getting the taglibs to work is taking some work (ie, it isn't supported), and it looks to me that Webwork2 is in a fairly similar state.

So here's a hint for framework authors: if your framework allows developers to use the same JSP taglibs in pages for both web and portlet applications you are going to pick up some quick marketshare.