There are many shops (in New York City at least) that still use Mason. Shutterstock being one of the ones i used to work on. While the infamous John Napiorkowski is working to port a number of web apps within the company over to the Catalyst framework, the bulk of the code still is and probably will be Mason based. Travis Beck and myself refactored a lot of non-Web based business rules out of Mason components and into Moose objects, and then used those Mason components to only handle Web stuff (form processing, redirection, etc.). This was a huge boon, and leaves me with a conclusion that Mason, while not as savvy as Catalyst is still a viably modern and robust solution. My current employer uses Catalyst and Moose, for what it is worth.
As always, your millage may vary and the responsibility of keeping the various parts of MVC separated is still very much up to you.