Most recent update from Runic Games:
The Mac port is taking a lot longer than we expected, but it's definitely still in development. Sorry for the delay!
Our devs don't have much experience making games for Macs, so we've had to contract the port out to external developers. The first attempt didn't work out, so we've given the project to a more experienced team. Hopefully they'll be able to finish the port and iron out bugs pretty quickly so that we can get the new version to you, but we'll have to see what sort of problems pop up. In any case, rest assured that it will get finished. |^)
Again, sorry for the delay, and thanks for being so patient!