I still use PSP 5 to this day, its an amazing photo editor for 80% of the quick image editing tasks I do, and it is self contained in a folder so its natively a "portable" app.
I have a retail/boxed version of PSP7 and i really like how fast it opens. At some point i want to make my own "PSP clone" since i do not see any other image editor trying to use a similar UI (i think GraphicsGale is kinda inspired by it, but it is specialized to pixel art, not a generic image editor). But of course this is yet another thing for the "stuff i'd like to do" pile :-P.
My PSP5 is also the retail boxed version, one of my first few actual software purchases I made from way back. I'm also familiar with the "stuff I'd like to do pile" it sits next to the "games I have never played pile" both piles are quite large :)