I've been running a small server for several months with the same setup: Bukkit on Mac OS 10.7. A couple of days ago, I reinstalled the OS from scratch. I copied the server directory in its entirety, with no modification.
The server runs. I can connect to it from my computer using the local IP, but not the global IP. Assuming that it was a port forwarding issue, I checked the router. The port forwarding is set up properly, the server is at the correct IP on the LAN, and HTTP connections are properly forwarded and reach the server.
If I telnet to the server's local IP on the minecraft port (25565), it connects. If I use the global IP, there is no response, which is what one would expect were forwarding not working. When Bukkit is not running, however, then the connection is refused at either IP. If the port were not forwarded, the result should be non-reponse whether or not Bukkit is running.
For testing purposes, I completely disabled my firewall.