I have banned the whole of the amazonaws network from my site. Not only have I seen a bunch of questionable crawlers coming out of them, but I have also seen tynt.com (A nasty, unregulated web proxy, that not only duplicates your content, but gives hackers free reign to probe and jab your site with impunity) come out of amazonaws.
In my opinion, most servers, do not have any business surfing a website, and 95% of my attacks from named domains, have come from such.
Personally, I use my own freeware GPL site wrapper rather than .htaccess to ban them, and the reason I landed on this forum was, I was doing research to make sure banning amazonaws from my site was a good idea. I see I am right, thanks to you guys, so the signature stays.
btw, if ya wanna take a look at the wrapper it's at This Link.