Depends on how you define art and popularity. Commercial art and illustration, there’s a huge number of print and TV ads, kiosk applications etc. using 3D that people aren’t aware or don’t really think about. Medicine, forensics, military training, education are all in there with the huge entertainment market. If you look at the 3D Warehouse, SketchUp has probably increased the production of 3D architecture tremendously. Affordable 3D scanning/printing is probably going to be another big area.

If you mean ‘fine’ art,’ ala Poser, it’s certainly growing and maybe attracting some people who might have done ‘traditional’ painting, sculpting etc. in the past, plus others who would have never gotten into art at all if it weren’t for 3D. How popular it is, either in absolute terms or relative to something else I don’t know. Bing/google may give some indication, of the number of sites and their traffic, but you can find a ton of anything on the internet. As false1 said, it also depends on whether you’re talking about users or viewers, i.e never have so few rendered so many naked Vickies for so many ÷)

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken