I'm still unsure when to use
Bitcoin and when
bitcoin is more appropriate. Did anyone define when to use the word Bitcoin with a capital
B? Is one used to talk about the currency as in "3 Bitcoin" and the other for the "bitcoin protocol"?
From Introduction on the Bitcoin wiki:
Capitalization / Nomenclature
Since Bitcoin is both a currency and a protocol, capitalization can be confusing. Accepted practice is to use Bitcoin (singular with an upper case letter B) to label the protocol, software, and community, and bitcoins (with a lower case b) to label units of the currency.
So, the accepted usage in your example would be "3 bitcoin" and the "Bitcoin protocol".