I am also running 10.6.4.
Whenever I connected the UNO, I would get a message about "New network interface has been connected but not configured." I kept hitting cancel or ignoring it. Finally I clicked configure and was brought to the Network panel of System Preferences. Clicked "Apply" and closed preferences.
After that my profiler says then when Uno is connected:
Product ID: 0x0001
Vendor ID: 0x2341
Serial Number: 649383233313512172C0
Speed: Up to 12 Mb/sec
Manufacturer: Arduino (www.arduino.cc)
Location ID: 0xfd340000
Current Available (mA): 500
Current Required (mA): 100
And a new /dev/tty.usbmodemXXXXXX device shows up (with a /dev/cu counterpart.)
You might re-connect it and check System Preferences -> Network to see if you have a Arduino Uno interface listed.