SB is cheap, at only like $97 ($57 through BHW) and its only a 1 time charge. So there are a LOT of people using it! 95% of those people don't really know how to use it, and they are all using the sources provided to obtain their proxies. Proxies aren't just for scrapebox, I have been using proxies for years, way before I ever got into marketing. So look outside of the Internet Marketing world for your public proxy sources. There are many sites and forums around, and some of them you could even put the URL into scrapebox's source lists and have SB scrape your custom sources for you. Then your lists will not be like everyone else using SB incorrectly, which results in lower performance for you.
Here is a scenario... Some newbie opens SB, harvests the default sources for proxies and checks them. Then he does a blast to 500k wordpress blogs. By the end of his run, he is scratching his head and wondering why he is getting a shitty successful post count. Weeks later, wondering why he is still struggling to get backlinks... well, by the end of his 500k run (using 180 proxies from SB that were "good" when he checked them), all of the proxies are noticed by Akismet now, and every time they are used to post to WP it instantly goes into spam....
So then you come along, slightly smarter and more experienced than the newbie before you.. You have a smaller, but better quality list.. Took the time to gather a nice sized comment list, highly spun. You got a large list of random names, emails, and enough websites in your list to post to. (don't just use 1 url in the website list, you need to at least have a handful so it sin't the same website everytime!).. but you run your blast.. and your results suck.. it wasn't you, it was the idiot before you killing the proxies..
Moral of the story, delete every source scrapebox comes with and go get your own.