well NURBS are a pain in the arse, mainly cos you can't add detail locally, and then trying to work with patches to keep the detail local, then having to make sure they're all tangent is a nightmare.

As someone said, they render a whole lot faster in PRMan, which I guess is the reason they use them most in production, but of course now SubD's are taking over: Monsters Inc was done with SubD's too. Also Maya works a lot faster with NURBS in the viewport: Maya is designed to be NURBS software, after all you can't use paint effects on polys and fur on polys is a nightmare.

For me the best workflow is model and animate in Polys then convert to SubD's for rendering. The only place where this falls down is that polys are a nightmare to texture but in Maya 4.5 that's going to be fixed: You can convert your SubD surfaces to NURBS, which essentially means you can convert polys to NURBS! joy and rapture!