My other car got rear ended, so i bought another bumper off a junkyard. I painted it myself, and it came out ok. Some things to remember is to get the whole thing nice and smooth or it will show through, and another is you can never have enough clearcoat i only sprayed like two coats and you could tell it was darker and not too shiny. (but you had to look real close to notice)

 

yeah man, my trunk did the same thing. when i first got it, it was used, so i applied some touch-up paint on various spots of the body where there were very minor chips. when i sprayed where the license plate lights are located on the trunk, the paint all around them just started peeling like crazy. i'm not sure how i got it to stop. it doesn't look too nice there, but it's a place on the car that no one looks, so i figured i'd let it slide. i asked a couple people about what the hell happened and the most common answer was that the trunk must have been replaced and wasn't prepped correctly during the repaint. i've never have a problem when washing it though.