Under intensive audio work (plugins) the new mac processor load stays very low (a few percents where the MDD G4 was near the limit), and the tasks are well balanced on the cores by Logic. The fan doesn’t run faster and the computer doesn’t turn hot.
The integrated converter sounds warm and with an interesting color, despite probably not being as clear, and not allowing as low latency as a pro audio interface. There is still to compare it with an Apogee Duet to conclude, hoping not experiencing the hiss noise some users did (for most due to a ground loop through the audio wire).
Sometimes the Finder quits without reasons (when opening a disk image), and it also did many times while browsing/opening plist files in user/Library/Preferences (seemed due to two bad preference files whose creation/modification date is 2009 – no hints on their role).
Sometimes the system writes data (more than 600 Mb for a basic use) without obvious reason, and is then more disturbing than the very quiet fan. The resident memory is also huge (700 Mb – was only 150 Mb on the G4), in part due to the shared video memory (256 Mb), however it should be less.
Performance on games was great : Tomb Raider Anniversary demo, Lego Indiana Jones demo, and even Bioshock demo played very smooth in 1680×1050 (default medium graphics details for the later). The rendering was a huge step from the G4’s Radeon 9000 Pro (water textures and effects).
Crossover 9.1 allowed to play old Jedi Knight (DF2) demo perfectly in 1680×1050 (through activating the 3D accelerating in the game options), despite 2D option screens (and cutscenes) not rendering correctly (bad colors, and then close to unreadable text) – no problem for in-game (3D).
However the half back case was very hot (probably more than any macbook or imac) after playing 45 minutes of the most demanding demo. In fact the fan didn’t seem to run faster when playing, and those over-heating could lead to problems.