I think Matt Cutts said that the process could take several months. With 700,000 sites that got the link warning message in Webmaster Tools, and that only representing a fraction of the sites that were hit by Penguin, Google could potentially be looking at millions of Disavow Link requests that may have to initially be processed manually.
I also see it as a method to collect lists of backlinks from sites that will likely eventually get banned.
"It's inexcusable for scientists to torture animals; let them make their experiments on journalists and politicians." -Henrik Ibsen