for me, bitcoin is a way of investment and not yet a cash. Bitcoin can be used as payment for online services and transactions that cash couldn't pay for.
main difference is actually cash (governmental currency) is centralized and crypto currencies (starting with btc of course) decentralized which provides anonymity.
I think this is a good comparison, however the government still want to regulate this decentralized system which might not be
favorable for us as for sure they will not allow bitcoin to replace the current centralized system they build.
But we own our money, we can exchange our money to Bitcoin anytime and that is also one of the reason made the price of Bitcoin increased a lot of value in this year without much good news. As long as the people still want to using Bitcoin, the government can not kill this currency.