Forgive the bitter headline, but I'm sick of Mac game companies releasing games, especially ones as massive and significant as Quake 4, without a demo. This gripe is further compounded by the fact that the current state of Mac gaming is so demanding of hardware; yes, it's certainly improving, but many of these games require a PowerMac G5 or, now with the Intel switch, at least an iMac or a MacBook Pro to run them with any decent amount of detail and frame rate. Releasing $50 games without the ability for users to test them first is shooting oneself in the foot, and apparently, companies like Aspyr seem to have no shortage of feet.
With that small bit of editorial out of the way: Aspyr has (finally) released a demo of Quake 4! Hooray! Both a torrent and a direct download link of the 536MB Universal Binary demo are available from MacGameFiles