1. Open up Image Capture
2. Go to Preferences and click the option under "Scanner" that says "When Image Capture is launched, open scanner window"
3. Then in the Scanner window, click on the "Options..." button
4. Then click on "Buttons"
5. Make sure "CanoScan Toolbox 5.0" is specified for "Application to launch when scanner button is pressed"
I did all this and what (incorrectly was always happening when I pressed any button on the scanner was that Image Capture started up (along with the Scanner window), and that was it. What was supposed to happen was CanoScan Toolbox was supposed to launch and initiate the action associated with the button. Here's how I fixed it:
1. Followed the instructions in the 1/2/2008 posting here, (I think he means Jan 9th Canon install tips, which several other Canon users found useful.-Mike
) uninstalling both the driver and toolbox (including any of their pref files I could find, emptying trash, and restarting as specified) and then reinstalled the toolbox first then the driver.
2. At first I didn't do the "Save" step (open toolbox, and then click the "Save" icon) and the behavior of the buttons was unchanged (and incorrect).
3. Then I did the "Save" step, but only clicked on "Apply" on the dialog box that then pops up. The behavior was still unchanged (and correct).
4. then I did the "save" step again, but this time followed it through until the end, clicking on the "Save" button in the dialog box and letting it save the scanned image in a file. This time, the buttons worked as they are supposed to!!! Hitting any of the buttons launched Toolbox and performed the correct actions associated with the buttons. In fact, it worked better than the Canon tech support people told me it would work. They told me that only the 3 right-most buttons work with a Mac and the 4 left-most buttons would only work with Windows. I've found that all the buttons work. However, Toolbox doesn't seem to reflect the mappings of the 4 right-most buttons in its user interface (and doesn't let you change the mappings, like you can for the 3 right-most buttons).
Anyways, in summary, the key for me was doing the "Save" step, but doing it completely (by letting it save a file). I don't think this was clear from the other comments. Hopefully this info will help someone else.