Quote from: majamina on March 30, 2015, 10:13:07 PM

But there are no coins, just balances on addresses. The darksend process removes any association between two given addresses. That's where the fungibility comes from and that's the question I asked. Where is the 'taint' you talk about?

Let me rephrase: Due to the nature of a transparent blockchain, there will always be associations with addresses, even if your concerned association is eliminated. People won't mix because they don't think they need to, or maybe they aren't aware of some illicit trade 80 transactions up-chain. Because of this, we will still see increasing use of blockchain analysis and increasing discrimination against transactors that leads to fungibility issues. The only way to eliminate this concern is through an entirely opaque block chain.

Quote from: majamina on March 30, 2015, 10:13:07 PM

For me, fit-for-purpose would mean working, useful services (instant transactions, privacy, 2FA etc) which are secure against any realistic attack (i.e. not guv/TLA).

Okay. Then in my opinion, yes, it's probably fit for purpose right now. But as demand for blockchain analysis services increases, major fungibility issues will start to pop up. Of course this won't be provable until it actually happens.