I received this response from Canon:
"Thank you for writing to us. We value you as a Canon customer and
appreciate the opportunity to assist you. We regret the scanning
issues experienced with your PIXMA MP810.
The pre-installed drivers included in Leopard can be used for printing
from Leopard.
Note that Easy-PhotoPrint will not work with the pre-installed drivers
although there is no problem with Easy-PhotoPrint EX. Therefore,
upgraded versions of the software and printer drivers will be released
and recommended.
Limitations with current MP Navigator (v.2x / 3x) / MP Navigator EX on
Mac OS X 10.5 will prevent scanning into these applications. It is
recommended to use ImageCapture or other TWAIN compliant application for
scanning. Additional information will be available as it is received
and will be posted along with all updates on Canons website at
www.canontechsupport.com.
I apologize for the inconvenience. Please let us know if we can be of
any further assistance with your PIXMA MP810."
At least they know it an issue - hope they fix it because image capture and photoshop both cause the scanner to freak out and freeze.
If anyone knows of a temp solution, please let me know.