Well I've been playing around with it for some months now and I can't say it's fast because I'm not interested in optimizing my scene at this stage, I just want to get used to using it and putting it through different lighting and surfacing set ups. I'll also admit I didn't get into Maya so I could learn Mental Ray so my opinion is is not balanced. But I think Vray is exceptional and the learning curve is not very steep at all, that's the whole point of it. From the word go I saw a level of believability in my renders that I never had to struggle to get. There's a lot of tutorials that cover good production settings and even the 3DS tutorials are valid as the UI is more or less the same. If you can get into it then I think you should. Nothings perfect, but I see more positive about it that negative.