Seeking Topics for a GNU Developers Book

Eric Harlow writes "Looks like I'll be writing a book for the next few months on gnu development using Linux. I've convinced a publisher that it's necessary and that there's a market for it - and they're going to take a chance on it. I want to gear the book towards the growing number of ex-windows programmers as well as up and coming list of Linux application developers. The book is going to focus on database and gui development with Postgresql and GTK+. I was wondering if there were other topics that people wanted covering or thought it would be a good idea to cover. I also was going to talk about PHP, CGI, CORBA, and maybe threading - but I don't want to write a low-level book. I think that Linux needs application developers and I want to write this as a starting point to help people write some serious applications for Linux, primarily GUI and internet. Suggestions on topics appreciated since I have to give the publisher a finalized table of contents soon when I hand in my first chapter. -Eric "