[important note, as of 4 Sept 2010: Google Wave will not be available as an end-user application after 31 December 2010.]
People have the tendency to judge a software by its user interface (UI).
Think about it. Most users probably don’t care about your network protocols or what your server topology is. Those users will, however, think it’s awesome to drag and drop documents and pictures from location to location. Most folks are used to this since most of them interact with Facebook, Twitter, and all the like. They’ll probably think it’s cool.