Yeah, it looks like it's not quite activated for all users but will be soon.
Also, I generally just immediately transfer my funds over to GDAX to place my order so I don't incur fees. That's likely not going to be changing so if you want to take advantage of this you'll have to pay the crazy Coinbase fees.
Still, nice to know it's an option when you see a crazy good buy opportunity.
RE: News to Note - Coinbase just announced instant bitcoin, ethereum and litecoin purchases