When heating with an air-conditioner, the efficiency is not too good, but not too bad. 1 kWh electric energy = 5-6 kWh heating energy (equivalent). So there is a ratio of 1:5 to 1:6.

When heating with just electricity, the ratio is 1:1 (1 kWh electic energy = 1 kWh heat equivalent).

In the end: nice joke from Microsoft.

It took me some time to understand what BitCoin actually is.

Basically, BitCoin network is a big transaction database.
One transaction is: "transfer X amount of BitCoins from account Y to account Z." This 'database', or transaction log is replicated and stored on all participating users' computers.
You can be sure a (your) transaction has been recorded, because you can check with many other peers who will verify that it is.

Of course, the inner parts are more complex, and there's a way to generate new BitCoins (but over time you can generate less and less, so it's a finite amount in total).

(I forgot to login before my comment, so i'm posting it again.)