I know I haven't been around in quite awhile, but I've been busy writing a couple of books. The book that's most relevant to this forum (and this is an unabashed plug) is an eBook called Using GIMP, published by QUE. The Using series is brand new, which caused a few extra bumps in the road when I was doing the writing. It also incorporates eBook text material, screencasts, and audio sidebars, so it's learning by multimedia.
I expect the book to become available by late June or early July. It's a book for the very beginning GIMP user on a Windows OS, so advanced GIMP users on Linux or Macs may feel it's a little light. Nevertheless, I think it's a good place to start for someone who has little to no experience with GIMP and wants to get their feet wet.
I posted some screenshots of a couple of the PDF pages from the front matter in my latest blog post. I still am writing another book, but I hope to spend more time here as the book launches to get everyone's opinion (be nice) about it and to share other GIMP and graphics related projects I'm getting into.