How about the drag&drop installation of an application anywhere in the Filer? The only platform where I've seen anything remotely resembling that is Mac OS X and the ROX filer (which incidentally also provides drag&drop saving). ROS even allows for the installation of an application inside another application! I love it, like practically all the other drag&drop functionality of RISC OS. It gives me a sense of freedom and control over my desktop, while also providing scope for a more intuitive handling. While chatting, it's lovely to be able to directly drag a URL out of NetSurf's URL bar using the Ctrl key and dropping it in a chat window. Conversely, the ability to simply drop a Text file containing a URL onto NetSurf's URL bar is just as useful. Among other stuff, I believe especially the drag&drop concept as seen in ROS makes navigating and using the desktop so swift. Essentially, a user may have more of a unified desktop experience, ie. the whole desktop being one interconnected application. I believe Herbert zur Nedden hit it on the head when saying -- "The main benefit of drag and drop is that you work with the data and not the applications to handle your files."
By the way, in the article Richard Hallas stated "that while RISC OS pulled off drag and drop first..." which is inaccurate. The concept of drag&drop is quite old, possibly going back to Engelbart's GUI designs of the 1960's. What can be said, however, is that RISC OS probably was the first that implemented a refined, widespread and consistent use of drag&drop and, surprisingly enough, still is unique in that aspect.