I was thinking about the person that accidentally sent about 300 btc as a fee and .001 as the transaction amount, and it occurred to me that some simple logic could be put in place to avoid that. Just add a check to see whether the tx fee is larger than the amount being transferred and if so, either warn the user or reject the transaction or whatever. I don't recall what wallet he was using, but I haven't heard that any wallet has such simple logic yet....