I was quite surprised at the size of this book, considering that it only covers GTK+ and not also Gnome. Not only that, but despite the cover blurb's, 'Leverage the full power of Gtk+ 1.2, GLIB and GDK', the latter two libraries get little more than a passing mention. I consider omitting full coverage to be the worst fault with this book, because GLib provides most of the types, structures and utility functions that are not concerned explicitly with GUI building and GDK provides low level graphical routines. A good knowledge of GDK is necessary to display graphics and text in ways beyond the widgets provided by GTK+.
The good news is that the coverage of GTK+ is detailed, very well researched and accurate as far as I can judge. However, it isn't just detailed, it's positively verbose and usually gave me the impression that I was wading through waffle before getting to the point. No wonder the book's fat for its scope. This makes it rather awkward as a reference, but also ponderous as a tutorial and the order of presentation of some material and lack of exercises, also work against it as a tutorial.
With the publication date, one might have expected the author to have access to at least a beta of GTK+ 2. Now that version 2 has been released, books on GTK+ 1.x could be seen as obsolete, but the bulk of the API has not changed significantly.
There are plenty of code listings, but unlike the prose, they're brief and to the point. They're well laid out and labelled with line numbers to make them easier to reference from the text. I generally like listings, provided they're done sensibly, as in this case, because it means the book doesn't have to be read in front of a computer. However, errors always seem to creep in and this book is no exception. One listing that was supposed to demonstrate debugging had even had its deliberate bug accidentally fixed.
I would have given GTK+ Programming in C a 'Highly Recommended' award if it covered GLib and GDK and was written more concisely, but I think its flaws are too serious to be overlooked.Java etc.