I use the Gimp in my work on a day to day basis, and I thought I knew it pretty darn well. But this book has changed the way I work. It does have very good info about colorspaces and color correction, and I picked up a few things I didn't know, but for me the most valuable sections were about making selections. The section in chapter 4 on using the threshold tool to quickly make a selection mask knocked my socks off! I'm using this technique all the time now.