I could try to be profound and raise questions about editing historic photos, whether this makes them less valid as historical documents, etc. However, some of my classmates have spoken much more intelligently on the matter than I think I could just now, so instead I’ll refer you to Lindsay and Sheri’s posts, as well as David and Geoff, who contextualize image editing from a public history/museum standpoint.
My concern after this week’s videos and book about photoshop is, I’m afraid, far more pedestrian. I have long been aware that good editing can improve a photograph. My father, an avid digital and former semi-professional photograph calls this “developing” his pictures, or working in his “darkroom” (aka his iMac’s software). My friend Kelsey has put up photos on flickr which show the variations which can be produced through good editing.
I suspect that there is not a lynda.com video or book out there which can help me figure these things out. Rather, as Claire notes, it takes time and a lot of mucking about until things start to make sense.