That's what I had thought, but the only thing that has changed between when I could upload under either OS and when I could not was the update (I foolishly updated both OSes at the same time).
What's weird is that the first time I tried reinstalling the FTDI driver, and then restarted the IDE, at first there were two USB ports showing. I tried using one, and it failed. Then when I went to try the other, both had disappeared from the list.
One other thing changed between working and not working, and that is that I disconnected one of the two USB cables I was using on the Ubuntu machine so that I could try to upload from the Mac. But it was not the one connected to the port I had been using to upload from the Ubuntu machine to the Duemilanove, so it shouldn't have any effect.
I'll try polling for the device as suggested when I get a chance.
Thanks for your help.