With the lull in Bungie-related news that inevitably occurs in the void between releases, the natives at HBO have been getting a bit restless in their search for new information.
This search is referred to lovingly as bugging Matt .
Every once in awhile Matt decides to put down the uprising, as he did in this post, which primarily consists of answers to questions about releases with the simple phrase WID (which I assume means, When It's Done , the only official Bungie release date that has ever existed).
However, he did have this to say about Mac/PC Halo:
The last build I saw was really nice, by the way. Much left to do but still playable and cool.
So, we don't know when it first became playable, but it is playable now, half a year or more away from the expected (unofficial) release target.