Maybe very slightly off-topic but for those who are not familiar with what mental ray can do and why a "virtual photographer" could dream of having it (or a similar render engine like mental ray or yafaray): http://vimeo.com/7809605 (if you like CG or even simply photography it's well worth watching. In my opinion, one of the most beautiful 3D piece ever (yes, if you wonder, it's all 3D)

As for dictating what people should use, I guess no one want to do that here, we only share experiences and talk about the various solutions avaiable, what they offer, how realistic they are (not as "realistic render" but realistic to use). After that, of course everyone is welcome to experiment :)

NB: by posting this movie, I don't mean to say: "here is what you could do if you had vray". This is an amazing piece of art made by an amazing artist who truly master his tools. It's like Poser, you see some extremely beautiful renders made by gifted artists who master their tool, and you see a lot of less successful attempts.