(see bottom for OS X 10.8 Mountain Lion info)
If you’ve had any trouble running Canon EOS Utility on Mac OS X 10.7 Lion, you’ll be happy to know that a new version of EOS Utility was just released, and it’s listed as supporting Mac OS X 10.6.8 and 10.7. To download it, go to the Canon USA Digital SLR Cameras web page, click the picture of your camera, and then click Drivers and Software.
Although it isn’t necessary to install the Canon software if you use software such as Lightroom, Aperture, or Camera Raw to import and process your Canon DSLR images, you may find Canon EOS Utility easier for a few things such as tethered shooting and camera configuration.
[Update on October 4, 2012: Changes to USB device handling in OS X 10.7.5 may have broken Canon tethering, according to this blog post: OS X 10.7.5 breaks Canon tethering]
OS X 10.8 Mountain Lion update
Canon now provides a Mac OS X 10.8 choice in their Choose Operating System menu. As I write this update (September 2012), the only downloadable item listed is the latest firmware update. Other categories say new software will be available in October 2012, so you should check it again.
[Update on October 2, 2012: Canon EOS Utility version 2.11.4 may crash on Mountain Lion when tethering a Canon 5D MKIII. For details, see this post on another blog: Canon software crashing on OS X 10.8]