Yes, Bitcoin is vulnerable to a quantum attack. The most vulnerable are the coins with published pubkeys. It's about 4 millions bitcoins, that will be hacked and sold at the exchanges, that will crash the price to 0$. Coins at one-time addresses are vulnerable too, because when a holder spends them, an attacker has about 10 minutes to crack private key and perform a double spending.
There's a world of difference between those two situations. The existence of sophisticated QC doesn't make cracking keys instant. It's pretty much accepted at this point that Bitcoin's signature algorithm could be broken in a few years, perhaps ten years in a best case scenario. But it'll take much longer than that to develop QC that can do so
in the time it takes a transaction to confirm.
Also, Bitcoin users don't expose public keys unless they're spending. Until they spend from an address, the only thing exposed is a
hash of the public key. So we're mainly worried about people who reuse addresses and people who have exposed public keys (to third party services or via Pay-to-IP which was removed from the reference client several years back).