libftdi-devel has a missing requires. The header file /usr/include/ftdi.h has #include <usb.h>. So presumably libftdi-devel should require libusb-devel, which contains /usr/include/usb.h.
libftdi-0.15-3.fc9 has been pushed to the Fedora 9 stable repository. If problems still persist, please make note of it in this bug report.
libftdi-0.15-3.fc10 has been pushed to the Fedora 10 stable repository. If problems still persist, please make note of it in this bug report.