I am passionate about natural cordage and I feel that too much synthetic cordage is used within modern bushcraft for the bowdrill. Personally, I feel it is a bit of a cheat and you may as well use a lighter! (shock horror!) This clip talks about natural cord alternatives and demonstrates 3 different ways of using 3 different types of natural cordage, and shows that it isn't that difficult at all. I hope this encourages at least 1 person to switch!
Here is a short video demonstrating how to successfully use weak\thin cordage with the Bow Drill.
I have finally got around to making my own cordage - I started with nettles. This is a very good article which I used - http://www.jonsbushcraft.com/Nettle%20cordage.htm .The only thing it didn't mention was how many fibres to use - I started with 10 fibres for each "strand" and that made a nice thick cordage - you wouldn't want it much thicker or much thinner than that. My ember's weren't great but I think that was because I was being a bit gentler than usual and the cord could have been a bit tighter but as you can see from the pictures, it lit the ember (it's not allways about the size of the ember but your ability at lighting the tinder!) I just need to practice a bit more and get more confidence in my own-made cordage. I found the preparation was the time consuming bit - making the cordage was quite quick - I used the rope laying method as explained in the above article. I will probably just use own made cordage for ceremonial use rather than everyday use.