Sorry if anyone was offended, I was just trying to make some (I thought helpful) suggestions. But I guess I'll just stop here and thank everyone that had a constructive attitude about it and tried to help. I did learn here that a lot of things can be achieved by using plugins, so I also have to give a big thank you to the contributors.
@Ash: I am a professional developer myself with some experience. I did not want to offend anyone, much less to put "deadlines" or "complexity labels" on the tasks. Again: those were just suggestions. However... It's true that I don't know the internal architecture of your product - you are correct about that - but if someone would ask me to estimate the complexity of a task consisting in hiding/showing windows at the touch of a key I would say easy. But that's just me. For the redo part I think it could be fairly easy or extremely complicated depending on the internal architecture and that's all I wanted to say.
I will play with the software some more - great suggestion - but again my interest was not mainly aimed towards image processing (effects and such), but image manipulation (moving pixels, painting/filling small areas) and that is where I thought there were things missing, compared to other software I used before. But I will be patient and wait for future improved versions of PdN that might fix it for me.
@brad.pike: Thanks for the advice . Yes that Repeat Effect command is what I'm talking about (and I was aware of it). But think of it applied to anything that makes sense to repeat (New Layer, Resize Canvas, Auto-Level, Black and White, ...). What you are suggesting on the other hand is "command history" (with redo, undo...) just like you have in highly expensive Adobe or Corel products - but only applied to effects.