On upgrade, warnings about undefined symbol TiffReadRGBAImageOriented in the tiff loader. (presumably running the pixbuf loaders update thing in %post) Maybe need to prereq a newer version of libtiff.
I added a Prereq: libtiff >= 3.6.1
Just got this on a FC3 box: g_module_open() failed for /usr/lib/gtk-2.0/2.4.0/loaders/libpixbufloader-tiff.so: /usr/lib/gtk-2.0/2.4.0/loaders/libpixbufloader-tiff.so: undefined symbol: TIFFReadRGBAImageOriented libtiff 3.6.1-7 was installed at the time.