The big problem was that you could forget to specify a "change" output, and then any unspend bitcoins would become the transaction fee. For large inputs this co

The big problem was that you could forget to specify a "change" output, and then any unspend bitcoins would become the transaction fee. For large inputs this could be a disaster. The 0.9 release candidate of bitcoin-qt now does sanity checks on the transaction fee, so this shouldn't be such a big problem anymore.