What happens if a miner or miners working on the current block get one transaction and x time later get another transaction which is a double-spend of the first while the block is not yet completed? Do they discard both transactions? Or what?

And what happens if the double spend transaction comes a block later? 2 blocks? 3 blocks? etc...    - I assume in those instances the latter double-spend transaction is simply discarded?


Then what happens if one transaction gets into 1 block by miner A. The double spend transaction gets into 1 block by miner B. If the time difference is not large it's hard to believe either would surrender to the other and both will try to continue their block chain for the time being to try and earn extra 25 BTC.

Just some thoughts I have. The probability of this obviously decreases with every block radically especially because un-involved miners will just go the faster block so the stack is loaded against miner B after just 1 extra block (his chances become nill and he has to go with the herd).