Can I reuse cedar grilling planks? Since wooden cutting boards are safe for use with meat, I was wondering if I can reuse the cedar grilling planks. 

Yossarian's answer to this question about how to prepare a plank says you can use one again depending on what you're cooking. 


So, what determines whether you can reuse the planks? 
How should I clean them after use?
After too many uses, will they lose the ability to impart flavor to what's being grilled?


The ones I bought were fairly expensive, so I'd like to get as much use out of them as possible.
I will generally reuse a plank on two conditions:


The bottom isn't completely charred. Sometimes, the bottom ends up complete black. I find that this won't start to smoke a second time. It's also a mess to store anywhere. 
The top isn't a mess of food. This is largely dependent on what you cook. Fish skin sometimes gets cooked on, glaze bubbles and chars, oil lights on fire and the top surface chars. Something like shrimp, tomato, or sausage will be fairly clean though, and nothing will cook on to the top. 


In order to reuse the plank, I clean it with soap and water, the same way I'd clean a wooden chopping board. I've never managed to use a plank more than twice and I usually just toss them after a single use. 

Keep in mind that a dried cedar plank is a dried cedar plank. Cost is generally more based on the store that you buy it in than the product you're buying. A hardware super store (like Home Depot) will generally have these quite cheap.