Ian did a nice job on the portal rewrite for ACS4. I can say that after staring at his code and documentation for a couple of days, but further evidence comes from the fact that the ArsDigita intranet rewrite was relying on it, and extending it to make it easier to use. Reading Michael Bryzek's notes (http://www.arsdigita.com/bboard/q-and-a-fetch-msg?msg%5fid=000Yu3&topic%5fid=935&topic=ACS%20Applications) about the intranet project are what made me consider the portal application an essential part of the toolkit.
Ian's implementation contains at least some of Michael's requested features. The APM should do a nice job of making it possible to share locally implemented portlets with other sites. There's a lot of flexibility for providing different layouts for portal pages, and I think this is new. The ability to create a "mockup" page containing static html is there.
The ACS4 version is more flexible with respect to where and how the portal pages are organized. You mount the portal package on a site node using the site map, and that constitutes a new portal page. The cms package I proposed works the same way: you mount it on a site node and then you can add articles to that node. So integrating the two packages would not be difficult.
You can download Ian's documentation for the 4.x portal package here.
Disclaimer: I have not built a site that uses any version of portals, and would enjoy hearing from anyone who has had that experience.
