It is a common problem when designing low-power CMOS circuits, to accidentally leave a gate floating [esp. in shutdown mode. I've had this problem :sad: ]. If you have a very large circuit, it can be hard to catch this problem, too (your simulator often won't indicate it's floating). Then after you have your chip fab'd, your test engineer comes back to you and asks why your chip is taking 1mA standby current instead of 1uA... it's a sobering moment.
Some people write plug-ins for their simulators which find floating nodes, by applying a tiny upwards or downwards current to every node in the circuit. If the state of anything changes, then you know you have a floating node.