I call Paint Shop Pro the poormans Adobe Photoshop.
It can actually use the majority of the same plug in programs, adobe has also learned from Paint Shop Pro as they took the browse feature and added it to Adobe (which was something I really liked in PSP)....problem I have is that many times if I use it in adobe it shuts the program down some.
However when you are using the tools section and saving the image (especially when you use layers) you can see the image quality difference between PSP and Adobe IMO....Adobe is clearly better in that area.
However PSP is much easier to use IMO and for the most part, for a person that does not need the quality or extensive tools of photoshop, in other words a guy that would never even scratch the surface of adobe, they are just better off using PSP.
I use both, I am now just getting back into adobe as I finally got enough room on the hard drive, but for years I used PSP.
I still like the browse feature better in PSP and I also like the way the fonts tool is setup better in PSP compared to Adobe....only because it is easier.
So if you use PSP and then find that you want better quality, then move up to adobe.
Oh one last thing, I like the animation program that comes with PSP...very easy to use when making simple animated gifs.