So in theory (I haven't checked what the API gives you control over - so this may be worthless), you could monitor your instance (bandwidth, time up, disk usage, etc), and if things get out of hand, or approach your limit (whatever it is), you could use the API to say shut down or delete the instance, or throttle the bandwidth (maybe via firewall rules or something?).
Again - this would assume the API allows you to do this (and ideally from within the instance itself - which shouldn't be an issue, I wouldn't think). And again, it shouldn't take this much work (you're right, it should just be a simple control panel setting).
But maybe it's an option for those who have the skills to implement it?
