I started using Darwin Ports when tools like hping3 and ctags didn’t work quite right on OS X. For example, the berkeley packet filter on OS X is totally different from the one on Linux, so hping3 wouldn’t compile correctly. Also, ctags in OS X doesn’t have the -R flag for recursion.
With Darwin Ports, I can install libraries and executables that don’t work quite right on OS X but work great on Linux.