After finally getting round to playing HL2 on OSX, I think I'm going to stop bothering with Source-engine games until I get a new Mac.
On Windows I run HL2 at 1280*800, 2xAA, 8xAF, everything on Medium (Shaders on High) to ensure a smooth 60fps. On OSX it drops to something*640, everything on medium, no AA, 4xAF and it runs at 30-40fps. That's not performance that I can "switch" to OSX for.
Its also not-so-great with dual monitors (under Windows I can just disable the one I'm not using).
Now... these smaller/indie games I'm all for. I hope we see a lot more of them turn up this week.