This is going to seem very rudimentary to most, but I found it to be awesome. I was in the process of removing the background of a photo for use in an advertisement. I used the Magic Wand tool in Photoshop to select sections of unwanted background, then delete.
While doing this, I started to notice a cool effect forming. The way in which the Magic Wand tool was selecting the various parts of the background was leaving behind artifacts resulting in a very cool "grunge" pattern. After getting the bulk of the background removed, I played with this new "effect" a bit; even copy and pasted some parts I really liked to increase the effect.
I think the result came out pretty cool. In fact, I think this was accidentally awesome!