Running Tiger 10.4.11 on a MacBook Pro; Audition 1.5 installs and runs.
Speed is more than adequate, subjectively superior to VMWare Fusion. All functionality appears to be present; recording and playback are free of pops and clicks. The app must be restarted when settings are changed in the OS X sound control panel, but otherwise integrates well, and even records from an external USB audio interface. Some text is in a font that's a bit hard to read, and some dialogue boxes are oddly sized, but nothing I've found yet seriously affects usability.
Overall, a great success. I plan to use this in production regularly!