Just worth noting, if you do share your key and it's found to be logging in from multiple locations some distance from each other in a short amount of time, which is evidence of it bring shared, the key can be de authorised.
Badspot does have the right to, but he doesn't do anything unless it's several people all at the same time, large distances away from each other, causing constant auth errors.
I have an 8k key that I use (almost) exclusively to allow friends to try the game. It's been used by a couple people in Texas, a couple in California, one in Florida, one in Ohio one in Quebec, until they decide they like it and buy their own copy
Another friend of mine gave his key to two of his friends, and for about a week they both tried playing at the same time and got constant auth errors
Neither keys have been deactivated