While using photoshop at college I noticed there's a handy little option
It would be neat if GIMP had something similar I thought.
Its a simple option that allows you to slightly blur the edges of pasted in objects so that outter edges are less pronounced (gives you choice of blur ammount).
Of course if pasted objects have other objects colors ect, from sloppy cut and past jobs then lol defringe still doesn't help. I had an idea to replicate this in GIMP requires many steps though wish I could automate the task abit.
Using selection to path then deselect once path is created then stroke path with blur tool (has alot more options then photoshop size opacity etc.

) plus if pasted selection contains unwanted colors like white edges you could use the same technique using stroke with eraser tool. Just wondering if theres a way to automate this task alittle more. I beleive it would be a very useful plugin for photo editing.