The one thing I hate and don't understand is that really few programs use power of GnomeVFS. Even GNOME Desktop parts don't use GnomeVFS for some reason, that reason is really secret for me. Of my currently installed programs, only Nautilus, Totem, Rhythmbox and Goobox use gnomevfs (I guess that's because GStreamer provides support for it). Also Text Editor (gedit) can Open files using GnomeVFS, but not save. Why? That's really annoying that I can't open a file from samba share not by copying it to local filesystem. Or save a nice web page to my friend's machine.
GnomeVFS is really nice library with clean and easy API. Why not using it?