The iSight doesn't work out of the box in Ubuntu. It takes some setup:

I haven't done this process in a while, but it's pretty well-documented on Ubuntu's wiki. I'll repeat how I do it though.

• Mount your OS X drive/partition. Remember the path to it.
• Install the isight-firmware-tools package:
  • sudo apt-get install isight-firmware-tools
• It'll walk you through the process. It will ask you to point to your driver file. Change the beginning of the path, which defaults to /MacOSX, to point to your OS X partition you mounted. In my case it was “/media/doug/Macintosh HD”. So I replaced /MacOSX with /media/doug/Macintosh HD.
• If all goes well, it'll extract the firmware and tell you: “The iSight firmware has been extracted successfully.”
• Shut down your computer completely, then boot it back up. Hopefully the iSight will work after that!

Even after you do this, some programs don't like it. For example, Firefox will try to make it work, but it'll crash. There's an easy workaround:

sudo vi /etc/ld.so.preload

Add this line:

/usr/lib/i386-linux-gnu/libv4l/v4l2convert.so

Note that this path might be different (substitute the proper directory in place of i386-linux-gnu) if you're on a 64-bit machine. This particular path works with my 32-bit Core Duo machine.

Run ldconfig (not totally sure if this is needed, but doesn't hurt):

sudo ldconfig

If you already have Firefox open, close it and reopen it. After this change, Firefox's flash plugin quits crashing every time I want to use the webcam. This change basically forces that library to be loaded when all programs are started up, and for some reason certain programs don't seem to be able to use the webcam without it. I haven't figured out how to make it work in Google Chrome, though.