Yes, they're likely converting most to fiat right now. The CEO has expressed this necessity given duties to investors as Overstock is a publicly-traded company. Bitcoin's volatility is indeed a problem in that light. Obviously that concern lessens as time goes by and bitcoin acceptance goes up.
This insta-convert-to-fiat period is a necessary step on the path to a more true closed-loop bitcoin economy.
And note that the CEO *does* believe in bitcoin for all the right reasons, and has expressed as much a number of times. Again, his post from Tuesday:
http://www.cnbc.com/id/101315433And check him out on twitter: @OverstockCEO