Don't forget Picasa, now also available for the Mac (to save us from iPhoto's insistence of managing the files). I haven't used PSP since the early 90s.
Most of the time for holiday shots and what not, something like Picasa is good enough, and the work-flow is much easier and faster (important to people like me who take 100+ photos a day). I drop back to Photoshop for piecing together panoramas and HDRs, and when it's better quality output is required on the few occasions, but by then, I'm down to an album of 60 or less (I don't want to completely bore other people).
I tried GIMP a few years ago, and won't go back to it. And for those promoting GTK - yuck! They couldn't even get the basics right, like the common file open/close dialog (and why they didn't delegate to the native versions on OSes like Windows is beyond me). Maybe it's improved since then, but I have no desire to change my current work-flow. It's courses for horses though: a lot of people around here like and support it, and good for them.