I have not used PSP (any version), mainly because I have always had access to, or owned Photoshop and/or Painter.
So it is hard to compare anything to it, but If I had none of the 3 and I was standing there trying decide which one to buy and money was not an issue I would go with Photoshop and Painter versus saving money and buying PSP8.
If money is an issue, I would probably not have the option to get anything but PSP8. I read on forums that a lot of people use it, so it has
The general rule of thumb with software is the more features, the more it cost. This is not always the case, and you can generally find out what the case is through internet searches and magazines.
If you have plenty of cash, Adobe Creative Suite is the way to go , IMO. that way you get a suite of software that works together and pretty much covers most of your bases in a image creation business.