Apple has released an update for its printer driver software for Canon printers and scanners. The update includes the latest drivers for Canon's devices, so if you have a printer from Canon, you might consider updating the driver, especially if you are having printing problems.
Keep in mind that while these driver updates may fix problems with working printers or provide support for new or previously unsupported printers, it will likely not fix the latest printer bugs found in Apple's OS X 10.6.8 update, which is more of a problem with the print subsystem than with the device drivers being used. Also keep in mind that if your printer is working fine, then you might consider avoiding the update. In the past people have found that updating their printer drivers has introduced problems in setups where there previously were none.
The update is a 307.39MB download from Apple's support site, but this package includes the drivers for all of Canon's printers. If you use Software Update, then only the drivers for your installed Canon devices will be issued to you. Therefore, using Software Update may be the preferred route for applying this update on home systems.
The update is for OS X 10.6.1 or later, and should not require a restart of the system to install. If you do apply the update and are experiencing problems, try resetting your print system by going to the Print & Fax system preferences, right-clicking the printer list, and choosing the reset option. This will remove your printers, and setting them up again should configure everything from scratch.