Well here in sunny London, I've got the slug working fien with OSX over USB.
However it was a bit rough. Kernel panics etc.
Here's what I did if it helps!
First I installed the driver.
Then I went to the Network Control Panel to configure everything. A little box came up saying something along the lines of a new Network port has been detected etc etc.... Clicked OK.
Now in the drop down where you normally select your Ethernet connetion or Apple Modem, ADSL Speedtouch has been added. I selected that.
PPP I left on automatic.
In the modem tab I selected Null Modem 11250.
Then in the Internet connect app I set my dial number to 0 put in my username and password and hit connect.
Nothing happened.
Restarted - Went to Network Control panel - Kernel Panic.
Restarted - Both green lights came on on the modem. Went to Internet Connect - Connected to the internet - surfed round for a bit.
Seems to be fine now. Hope this helps. I wasn't on my Mac when I typed this so exact details may not be perfect, but you should get the gist.
C YA