Using Darwin Ports to install libraries, I ran into a snag with cairo.  Although the ports listing said it had installed 1.4.14, when I tried to install py-cairo it refused, saying it needed a version of cairo at least 1.4.10.  After verifying a bunch of different consistency issues, I am pretty sure that the cairo.pc file just had the wrong string in it:  pkg-config believed the cairo.pc assertion that cairo was only version 1.4.10, and refused to continue installing py-cairo.