Well, they patched it and it works. Game runs great on medium settings (can't antialias on my newish iMac without massive slowdown, sadly; ATI 4670 isn't good enough, I guess).
The game itself is pretty good, I guess, but I have a hard time wholeheartedly loving games that requires as much jumping as Trine does. (Personal preference.)
Looking forward to more Mac offerings on Steam - waiting for a price drop on Torchlight...