Apple has released an update to its Brother printer drivers for OS X, which include fixes and enhancements to currently supported models along with drivers for new products from Brother.
The update is a 149MB download from the Apple support downloads site, but this download includes the entire set of printer drivers that Apple offers. If you have a Brother printer configured on your system and a new driver is available for it, then you can update just that driver by using Apple's Software Update utility in the Apple menu. The update requires OS X 10.6.1 or later to install, and does not require you to restart your system.
While this update is available and you might see the software update show up in Apple's Software Update utility if you have a Brother printer, if your printer is working fine then you might avoid this update for now. In many instances printer driver updates might fix some problems but introduce others for printers, so only apply this update if you have a notable feature that is either missing or not working on your printer.
If you have applied this or other printer updates and are now experiencing problems, try resetting the print system and reinstalling the printer driver. To do this, go to the Print & Fax system preferences and right-click (Control-click) the printer list. Select "Reset print system" from the contextual menu that appears, and then add your printer again. This procedure should clear the current printer configuration and replace it with a fresh configuration as Apple shipped with OS X.