I have worked with SAP Portal, Oracle Portal and Microsoft Sharepoint And you know few of my co-workers who worked on these platforms had a good word for them....
Let me explain. A portal is supposed to be an easy way of getting content onto the web, in a controlled and safe fashion. The problem is that Dreamweaver is quite easy with a little coaching, and raw html is more flexible than what the portals tools allow. Portals allow you to make simple pages with simple theme design. But for anything more specialised and bespoke, the amount of time trying to get your site to look precisely how you want it, multiplies by a factor of about 5 on web portals. Trying to get that extra 5% functionality always takes 30% more time, so in terms of time you are not better off than if you used a full web development framework such as Python-Django, ASP.NET or PHP-Zend.
Portals seem to fail more often than multiple sites on an old fashioned web server. I theorise that this is because they often feature pages packed with components (called variously portlets, iviews, web parts) each of which though small on the page is actually a full web application. So, many users loading many pages packed with many portal apps all causes the portal foundation (often based on J2EE) to crash. We have had a lot of trouble with our portal in BigCity Yorkshire as users packed the home page with apps all of which drew unaggregated data from one database. The strain on both the portal and the database proved too much.
Personally I think an organisation is always better off with a good content management system which sits on top of a number of technologies, and which allows those technologies to be mixed, matched and mashed. Also it is not a good idea to have many sites in one CMS instance, instead spread sites over a number of CMS installations.