Bit of a chicken and egg problem, really; if you're selling something, you probably don't want to be using bitcoin unless you're either a True Believer, or your product has extremely high margins and you're confident that use of bitcoin won't cannibalise use of more stable payment options. If you make a 5% margin on your product, you don't want that to be erased by a currency shift.
The big non-True Believer users thus far have largely been either illegal materials, or ultra-high-margin things (reddit gold, Humble Indie Bundle etc).