It Probably depends on location as well. From the amount of content they've produced it may be that Japan has a higher per capita use of Poser than perhaps any other country. I'm imagine that's probably rooted in their love of anime, manga etc.

In terms of user interest, I think there's a cieling on how many people want to create still, art type images. The future od mass use is IMO not in galleries but in a host of other online areas, FB (bah, can't even bring myself to spell it out :-), blogs every type of website, especially virtual worlds etc. The barrier is ease of use and Poser isn't, IMO, easy enough for that type of mass uptake. I haven't looked at iClone but it may be a move in that direction. Give a dead simple way to do avatars characters etc. and I think there could be a huge growth. I think people also want movement, interaction etc., so still imagery again has its limits. The fact that so few tackle animation, even in Poser I think says that the barrier to entry both in terms of skills needed and hardware has to come down a lot. The cloud will probably begin to answer the hardware part. You don't need state of the art cinema quality, at least to start with, but a simple way to do basic animation, set up interactive characters etc. Kinect type consumer mocap may be a big help.  

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