One reads about impressive dollar values for bitcoins and other crypto-currencies, but are they actually liquid assets? - something you could actually exchange for US currency or goods and services?

Most banks in the USA won't exchange foreign physical currency for US currency even though one reads about "exchange rates". I'd think bitcoins would be even harder to exchange.

Are bitcoins only used within a subculture? - something like the chips issued by a Casino that are only good within the Casino?