As a Russian speaking person, I do not pay much attention on Bitcoin and bitcoin. Russian grammar does not have that kind of differences.
You are not writing in Russian now, you are writing in English and you follow the rules of English grammar. 
so technically your example "My best friend doesn't see the advantages of Bitcoin." means your friend used the protocol not bitcoin as a currency. like if he created an altcoin based on Bitcoin.
My example has a double meaning actually. It can mean that my friend sees no benefits in using the Bitcoin blockchain. It can also mean that he sees no benefits in using bitcoin (the coin/currency). I should have thought of a better example, but I will leave it as it is now. I think either Capital or small letter B to use the word bitcoin it has the same meaning and understanding.
It doesn't have the same meaning and refers to two different things, hence this thread. But you can still grasp the meaning no matter if you use Bitcoin or bitcoin, sure. typing b or in small letter looks informal but Bitcoin should start with a capital B
It just looks weird to me to see bitcoin. Most of the time I just capitalize it. But I am glad I came across that survey and remembered an old discussion. Will try to respect the difference now anytime I can. I had a few PMs with GazetaBitcoin on this issue and that was my answer:
In that particular PM exchange, you are referring to the coin/currency as Bitcoin, when it should be bitcoin. I am sure it gets even more complicated for native Germans because they capitalize all nouns and unconsciously use the same approach when writing in English sometimes. Quote from: 1miau, PM
[GazetaBitcoin asked about my opinion on this issue]
Bitcoin (BTC) = Bitcoins
Bitcoin (BTC) = Bitcoins
But for BTC transactions it doesn't really matter because Bitcoin blockchain, doesn't really have ERC20 like ETH chain. So you wont mistake your BTC to a different address.
Wait, what?