I used OP's trap next to a spider dungeon in 1.5, works like a charm. The only issue is once in a while, string will get stuck on the half block nearest the collection point that I can't get, but it's rare enough to not be an issue.
Thank you to the guy on page 3 who posted each level individually. You're a lifesaver.
You guys need to look at the context. This trap design is from December 2010. The concept of using water to elevate a mob were fairly new and this trap design was a very good contribution at the time.
The goal was to kill all kind of mobs including chickens and spiders in the same trap and to have 0 item loss like you often get with lava. I think you are going to have a very hard time making something similar that works better than this.
Time goes on and we are now sorting mobs, burning pigs and rejecting spiders. A very different philosophy. It's unfortunate that some people keep bumpig this thread. It's an old design that had it's use, but it doesn't keep up with the modernizing of our biofactories.