Seeing as the thread was started a year ago, just to verify: Are you the only one currently working on the mac client? Just realized it doesn't seem to use NAT-PNP/UPnP due to the low connection count i got. With Bitcoin constantly in the news a lot of people who aren't comfortable doing manual port mapping (might not even run devices with static internal IPs) are probably trying it out now.
(A secondary but related problem is not mac specific: Not being able to run two Bitcoin clients on the same local network with one external IP without manual pass-through configuration)