The renderer in P4 is not as good as the one in P5, which is not as good as ones in other high end packages. But "pro" work can mean a lot of things. Who is your market, and what style are they looking for? Are you trying to save money/time from hiring a photographer or drawing an illustration by hand? Many people use high end renderers, but still pose the models using Poser. You'll see a lot of people here using 3DS, Maya, or Lightwave, but also using poser to control scenes. Depending on what you want to do, Poser may not be enough to do it all.