Big ones from saw mills are more like 15+ inches wide. The problem (as with any unknown steel) is identifying it so you can heat treat it properly and have reasonable expectations of how it could be expected to perform. If you have access to a lot of it, it might be worth the effort. You could send a sample away for testing or, if you like, you could do extensive testing of your own to figure out what it is - if you have the equipment.
Besides fillet and kitchen knives (both great uses), you may consider the thin stuff for small slip joint folders or for a hunters caping knife - almost scalpel like for working around lips and eyes.
It can be a fun undertaking, but if you only see it as free steel, the term 'free' will weaken from the amount of work you put in to figuring it out.
Rob!
