I can see Source coming to OS X but the computer hardware platform Apple provides leaves much to be desired.
In all honesty, I'm stuck with my current Macbook with no incentive to replace it.
Well with supposedly new, MBP's, Air's, and Mac Pros coming soon, this could all change. Perhaps we will see a dual launch of Steam client with MBP's..
a member on another thread that says he has inside information (maybe) stated;
there is going to be a media event on the 26th, where the iPad will be launched, along with Steam and the Mac updates to the MBP and Air (and Mac Pro? he didn't say)