Sorry for opening up an old thread, but this topic has come up for me in Az & I actually contacted a herpetologist for advice, which was, "Don't worry about it."
I ran into 5 diamondbacks on Second Water Trail in the Superstitions over a weekend. It was Fall (Fall & Spring in Az are prime rattlesnake season, I've learned). The herpetologist agreed this was unusually high.
In an attempt to comfort with statistics, he claimed that in that area I most likely came within 50 yards of hundreds of rattlesnakes without even realizing it. Also, that I was not bitten was evidence of the success of the rattle warning system.
My personal problem with this warning system is that it is used as plan B. Plan A is to be perfectly still and perfectly camouflaged. Plan B, therefore, does not take effect until well within striking distance. In my case, within inches of striking distance. The cool part is freezing at the sound of the rattle, only to be unable to locate the thing visually to know which direction constitutes "stepping away." And then convincing myself with statistics that, rationally, I should be able to fully enjoy the rest of my hike.
I will not sleep without a tent in the desert, and this is only due to snakes. I've been stung by scorpions more times than I can count, and if that were the extent of my concern, I'd sleep without a tent in a second.
Others on the trail have advised, "But they don't *want* to bite you! They're prey! They're more scared of you than you are of them! They're not aggressive, but *defensive*!" Good for them, I say. I'll take it all into consideration. From the inside of my tent.