For instance, you're laptop's wifi card is on, but you've deliberately not connected to any hot spots. Is there anyway it can be hacked while sitting there, and not connected?
It will still be scanning for networks, which means receiving and processing broadcast packets. It is possible for these packets to be malformed, and if the stack is buggy, then this malformed packet could trigger a bug and then compromise the laptop.
I've never heard of an actual attack using this method, there are going to be so few laptops in this state compared to the number actually attached to a network that it seems to be a very strange way to attack a system, but if you're worried, disable the wifi card when you're not using it. Of course, if you want to be really secure, you need a concrete box.