Quote from: bukaj on May 05, 2013, 06:44:26 PM

There are no users in bitcoin - only addressees

By "users" I simply mean people who use the system. While you cannot know what user knows what address, and not every address maps to a single user, nevertheless there are people using it.

Quote from: bukaj on May 05, 2013, 06:44:26 PM

and I'm not sure that all double spend attempts are malicious. Isn't it possible to attempt double spend during blockchain fork under "normal usage" - not willingly?

The old transactions would still be there, there would just be one more transaction type.

Essentially, the idea allows you to say: "I promise not to double spend the input of this transaction. If you catch me doing it, please pay this large fee to the miner."