What i'm doing is theming native widgets with the Plasma theme engine, to obtain widgets thet are usual QWidgets (and so offer the same API), but they draw themselves using SVG, like the majority of Plasma components.
In this video, there is a tab bar with a nice sliding animation when the active tab changes, and a button that has an animated glowing halo on mouse over:
The other thing I'm doing is a web browser that lives in the Plasma space. It is pretty basic, it has a minimal toolbar with a history-enabled address bar, the browser widget itself that remembers the last page opened and the scroll position, and bookmarks are syncronized with Konqueror. The web browser Plasmoid has been created both as a useful little tool to keep, for instance, a quick look on a frequently-changing webpage on the desktop, and as an experimental tool on how a very common application would look on a device that would have only Plasma as is main user interface (think about mobile devices for instance).