Hmm... should be working... I would say your Hardware->Troubleshooting issue is definitely related...
Have you tried re-installing the FTDI driver? The driver is at /System/Library/Extensions/FTDIUSBSerialDriver.kext . Deleting that file and rebooting seems to be the easiest way to remove the driver. The newest driver version is 2.2.10 and can be downloaded at http://www.ftdichip.com/Drivers/VCP.htm
I'm using the 2.2.9 version of the FTDI driver which came with Arduino with no problems, but I have an older Core1/32bit Macbook.
Once you get this straightened out, check out Arduino Playground - Cocoa . I wrote the IOKit/ioctl part, which lets you ramp up the baud-rate. You probably want the latest HardwareSerial(otherwise your Arduino can only hit 1000000 baud). Google Code Archive - Long-term storage for Google Code Project Hosting.