Yeah. I was playing at around 3 AM this morning PST. Everything was fine, and then Valve must have issued an update between then and 2 PM PST..
Of course, they issued an update right before I brought a few developer friends from Microsoft over to check out the Rift. So, I fired it up and sure enough, split screen goodness with no head tracking
Not before recompressing the GCFs and leaving us with an hour wait to 'improve performance.'
One of these days Steam...