Mac at Auld Golf has an interesting article about bent hickory shafts and when (or if) they need to be straightened. Good stuff from the Master.
There are a lot of little things to know about straightening shafts. First of all, why is it needing to be straightened? Many clubs were bent into the St Andrews bend on purpose. This added balance to a putter and made the lie angle flatter for shorter golfers. This bend is from the grip bending downward towards the club head. A lot of times I leave those clubs alone.