I had to use a digidesign sound card so I installed the appropriate driver and tried to open Pd. For a couple of times it hanged and I had to force quit it, but the third time it opened.
After a while I quit it and tried to reopen it and since then it just hangs. I uninstalled the driver (and its additional files in /Library/Application Support/Digidesign), restarted my laptop, but Pd still hangs. I tried to open it from the terminal with the -audiodev flag (tried number one as an argument, shouldn't that be the built-in audio?) but it still hangs.
I'm on OS X 10.8.5 with Pd-extended-0.43.4 (BTW, typing this in the terminal works: /Applications/Pd-extended.app/Contents/Resources/bin/pd -version).