Thanks for the response, from that I gather that there's probably not a way of doing exactly what I was talking about.
To explain a bit, I use Paint.NET a lot because it is very efficient at doing certain tasks - such as selecting particular parts of images and superimposing / manipulating these parts as layers. The software seems very well designed with a focus on making otherwise complex procedures simple, and thus maximising time efficiency.
I frequently have many images open at the same time and it keeps occurring to me that being able to have multiple panes on the screen at the same time, or even just being able to switch between open images rapidly with keyboard shortcuts would further speed up the kind of tasks that Paint.NET lends itself to.
I suppose a follow up question then is are there any keyboard shortcuts for cycling through open images?