JSF is an excellent technology to implement complex MVC related applications both in standalone web environment as well as in a portal environment.
We have adopted JSF exclusively to write a bunch of our applications here at JBoss. One of the applications that is being rearchitected using JSF/portal is our Forums technology which is currenly running on a framework called Nukes.
I agree, there are some implementation-level workarounds that have to be done especially with handling attachments, etc and the usecases you mentioned, but overall it fits like a glove for development on portal.
Also, there is support from the industry for JSF since there is already a JCP spec out there to build a standard-based bridge between portal and JSF technology. Industry support for technology you want to adopt for your overall architectutre is always a safe feeling.
My two cents