Everyone is using it as a countable noun. There's actually a grammatical rule that says this is what should happen. If a new term ends with an existing term and is semantically related to that term, it gets the old term's rules. If not, it does not.
So, a "pop fly" is not a type of fly (the bug). So we don't say "pop flies" but "pop flys".
A "bag lady" is a type of lady. So we don't say "bag ladys" but "bag ladies".
We don't say "two firemans" because while a fireman is not necessarily a man, the origin is directly related.
So, a "bitcoin" is a type of coin, the terms are semantically related. So it should inherit the rules of the word 'coin'. Since we'd say "one coin", "two coins", we would expect the rule to be "one bitcoin", "two bitcoins". This feels natural to people, so it's what they do.
The former seems to be the consenus. The two latter examples are rarely if ever used. They would be more commonly expressed as "how MANY bitocinS are used every day" and "600 bitcoinS is enough for this transaction". – DeathAndTaxes – 2011-10-17T16:28:46.300