When I first got Poser and felt the need to have content, I joined, and bought a lot of
things, because most were $1.99.  After a while I had so much stuff that it seemed
a waste of money to buy more.  It got to the point where all I was getting from it
was a hit on my credit card for the monthly membership fee. So I canceled it.
Now I mostly just grab the free stuff, or make my own content in Wings 3D.
If you don't have a lot of content right now or there is something really expensive
and you can get a good discount, it's probably worth it.  Just know when to quit
when you have enough.