or would you use a transaction-trapper, so you gets notified when your used coins gets re-spend? like tracking you coins?
There is the need for that -- something that connect to multiple nodes and listens for detecting double spends of coins received. Merchants accepting on 0/unconfirmed have this need.
- http://forum.bitcoin.org/index.php?topic=27417.msg350531#msg350531
checking for double spending is very eazy to check for, it only requites only you to connect to alot of nodes, and verify that OutPoints are only used once.