Nope. I think there's a danger of overthinking this one - nylon (or whatever they turn out to be made of) straps work fine, you can tighten them down and they don't stretch at all (as far as I can tell, from a 5,000+ mile coast-to-coast tour in 1998 and another one in 2003 across Minnesota). My straps still look as good as new, in fact, no sign of damage at all (maybe a little faded from the sun), and as Pete said, they are only a couple of bucks a pop. They are better than bungees, in my mind, because bungees stretch - so if you go over a bump, the sudden acceleration of the load can make things move around and even dislodge and fall off the bike without you knowing. A webbing strap is tightened down, and it stays tightened down (in my experience). Also, there's that whole taking-your-eye-out thing. I've had bungees snap up unexpectedly and almost cause me permanent and serious damage, so I don't trust them now (at least, not for high-stress applications like keeping a load secure).

I use a criss-cross method over the bags I keep on the rear rack (generally the tent, sleeping bag and sleeping mat). So each bag gets two straps, crossed over in an X on top. I first lay the 6 straps across the rack (under the rack, actually), then put the tent on lengthways (i.e. oriented in line with the bike), strap that down with 2 straps, then put the sleeping bag on top of the tent, crossways, strap that down with 2 straps, then the pad behind the bag, crossways, and use the last 2 straps for that. This way, the tent doesn't interfere with the pannier hooks as much, and the cross-ways bags are raised up a bit so you can still get into the top of the panniers while they are on the bike. Then I often use a couple of bungees, lightly tensioned (or a bungee cargo net, these days) over the whole lot, just to keep things like socks and bandanas which are drying. You can see this arrangement here:

http://www.crazyguyonabike.com/doc/p...580&size=large

As someone else mentioned, you may have to think a little harder for large items like canoes, where there is a lot more weight, potential vibration etc, but for the back of a bicycle... nah, these things "just work", any webbing strap from the Army Navy store would probably do the job.

Neil