check to see if there's enough for what you want to do with it, then see if the condition is ok - which kind of nails they used and if the holes are bearable. also check to see if the boards have warped from a water leak and/or poor storage not keeping them flat. of course, it's probably not an issue, but i'd check too if they're all the same thickness - or at least enough of them to fill a room. different rooms could've use different thickness and you may not have enough of one thickness to complete your job.
there are a million little things but like you said, if they look good, they're probably worth taking. i love old wood and you can't find it in the home depots, so it's good for restoring other older homes.