I don't, however, want to give the impression that this is a set of features that we've just been throwing into the pot only because the feature is cool. (Which, admittedly, it is. :) We usually do such things in Plasma with a purpose in mind, a use case. So here is one of our use cases for this set of features, and though many more such use cases can be generated it represents one of the primary driving forces behind this feature set:
"Plasma Pete is viewing his online calendar. Pete drags a calendar entry to one of his Plasma activities and he selects 'Event Tracker' from the menu that pops up (after Plasma has determined the kind of data that's been dropped, even though the data is from a remote source). The Event Tracker might even use Akonadi to show the information or it might just show a "web slice" of it. Pete notices that one of the events contains a typo, so he clicks on the 'maximize' icon that's right next to the configure icon in the widget's handle and up pops a site-optimized window that embeds his online calendar application. He makes the change, closes the window and the Event Tracker widget updates."
The ability to jump between widgets that display overviews and provide at most a small convenience interface to full feature applications (perhaps Event Tracker would launch Kontact, for instance), site-optimized containers for web apps or a generic web browser (and back again) will, we hope, tie the whole user experience together much nicer. This is particularly true, we feel, in more constrained devices / form factors such as netbooks but is also quite useful in the laptop/desktop space.