I've had the misfortune to be digging through a gnome program recently. The documentation is crap. Full of bad links, ambiguous statements and empty pages. Versioning is appalling, there is no list of documentation by gnome version.
When googling on the Qt4 api, I'll get a host of links to accurate offical documents, examples and informative blog entries. To a lessor extent it is the same for KDE (could do better).
With GTK/Gnome, 90% of the time I'll get a gnome.org page with broken links that is out of date.