I think this is a great idea - something I've thought about doing myself.
- You identified one (and by nature, others) when you asked for GIMP tips...perhaps an article on 'starting out with GIMP' and take us through some step by step on doing things with GIMP (or similarly complicated tools: Inkskape, Xara, etc.). The fact that you would be learning yourself provides you a great perspective from which to help/write.
- CLI/script tricks to automate tasks would be great/of interest too.
Look forward to reading!