Apple has updated their knowledgebase article on Aperture 2 wired tethering to include a list of Canon and Nikon digital SLR cameras
that the company has certified as compatible with this new feature. Notably absent are the latest Canon models, including the EOS-1D Mark III, EOS-1Ds Mark III and EOS 40D, among others.
Note: Tethering in Aperture 2 is a feature that enables photos to automatically flow from a connected digital SLR into an Aperture project, when the camera snaps a picture. Prior to v2, this capability required the use of other software and scripting alongside Aperture; in v2, with supported models, only Aperture itself is required. Some cameras, in addition to automatic photo import, can also be triggered from the Tether HUD in the program.
Also note that Aperture 2 tether support and Aperture 2 RAW decode support are separate things. The program currently supports a broad range of camera RAW formats, including CR2s from the three newest shipping Canon digital SLR models, even if it doesn't also support tethering with those same models.
Tethering in Aperture 2 has been widely discussed
in Apple's support forums. In addition, Apple's knowledgebase includes other articles on tethering: