Why can't OSX detect android Galaxy S for USB debugging?

Have you tried connecting the phone using a powered USB hub? I haven't tried it yet but found this blog post that suggests it may help for Samsung Galaxy devices.

http://esausilva.com/2010/10/02/how-to-set-up-adb-android-debug-bridge-in-mac-osx/

make sure that you plugin your device in the usb ports on the mac itself, not on the keyboard usb-ports.

Go to Tethering select and then deselct USB Tethering and you are done. this worked like a charm.