There have been quite a number of posts on Mashups now. Recently, Sun have released a sample implementation of Mashups with Portals. The sample code is good and it uses the Yahoo Map Api to develop the mashup. The Personalization features provided by portal can furthur enhance what mashups can do. They provide the RSS feed that one can add, to be displayed on yahoo maps.
This just shows a glimpse of how Portal can exploit power of Web2.0 and mashups. The end user can select his own mashups and personalize it to his own use. Though in this example the Ajax based api was used, it would be even more beneficial if Rest Protocol is used through Java. Take for example if we have Portlets for Google Calendar. We can have various such portlets which works on Rest Protocol and also uses the Power of Portals to personalize the things. There could be a way to single sign on, by storing important information in user preference data.
The above approach is to use Web2.0 content inside portals. The other examples in this regard would be use of wiki forums blogs with portals.
But the other approach is exporting the Portal data in form of Web2.0. I guess BEA Project Runner is based on such a concept. Its still under developement and we have to see what the end result will be. But this will allow the normal web-applications to be able to work with Portals applications.
Plus, we might wanna see the feature of allowing the portal to adapt itself according to the user interaction with the portal. Something like Tags etc.
Overall, i believe that Portal is truely the first step towards SOA, with Soap or with REST.
Your comments are appreciated.