I apologise if this has already been suggested...
Though I believe that there should be easier ways to rate applications for the 'software manager'.
If a user could 'right click' an application icon from either a KDE or Gnome application launcher to say something to the like of - 'rate this app',
I think this would be an improvement (in the sense that it would prompt me to rate the application).
Should I really enjoy an application - I would otherwise need to think - yeah what a great app, let me go into the 'software manager' and rate the app.
I don't want to do this.
Alternatively, there could be a 'rate my apps' option whereby it would still link to the the 'software manager' application, though it would automatically filter the applications that you already have on your PC,
allowing you to further filter down to the application that you have on your PC. You could then give it a rating out of 5. As soon as you click the ratings, it would allow you to add a comment.