It's still not earning you money to spend electricity because you still have to pay the transfer fee which is around 6 cents / kWh but it's pretty damn cheap nevertheless, mostly because of the excess in wind energy.
Last winter because of a mistake it dropped down to negative 50 cents / kWh for few hours, averaging negative 20 cents for the entire day. People were literally earning money by spending electricity. Some were running electric heaters outside in the middle of the winter.
Sure, but if there is too much electricity on the net, things will start to break. That electricity has to go somewhere. No one wants to buy electricity because everyone is trying to get rid of their surplus.
About the negative, I don't know.