[mriou]

> you can still feel pretty safe with 0 confirmations if you're monitoring the > bitcoin network for double-spend attempts over the average network propagation time

The above is much easier said than done. First, you're assuming you can have a good enough coverage of the network which is hard to assess. You need to do a constant topology analysis to see how well-connected you are. Second, you need to ask a chosen set of peers for all the transactions they have in their pool. And wait until they all reply. Third, you need to be pretty good at normalizing against malleability on all those transactions.

After doing all of this, the scheme is still not bulletproof. The blockchain exists for a reason.