It seems I could run the game just fine if I download directly from the humble bundle site and launch, instead of through the steam client (great game btw!).
Here is the "System configuration" part of the crash report, including graphics card:
Model: MacBookPro4,1, BootROM MBP41.00C1.B03, 2 processors, Intel Core 2 Duo, 2.4 GHz, 4 GB
Graphics: GeForce 8600M GT, GeForce 8600M GT, spdisplays_pcie_device, 256 MB
Memory Module: global_name
I tried the Verify Integrity, but still got the same error.
What is the difference between launching from Steam, and launching the one downloaded from humble bundle site?