What I've read about Poplar is that it's readily available, inexpensive (compared to PO Cedar), straightens easily and stains easily. I have made a few shafts from Poplar board bought at Lowe's but it was labor-intensive and the spine was variable. I ended up going back to buying Cedar shafts. I'm getting to the point where I will need some more shafting soon and realized that Rudderbows offers the Poplar shafting at almost half the price of PO Cedar. Looks pretty good to me, so I'll give it a try. Disadvantages of Poplar, it doesn't have that wonderful Port Orford Cedar aroma while you're working with it (or a consolation when a shaft breaks). Other than that, I don't really know of any.
Muler.