Here's how I look at it, if you legitimately want to use the disavow tool for a site that you own, it's probably already been hammered by Penguin or an unnatural links notice or both. Which means, sending in a list of your shitty, spammy ass links to Google ain't going to be breaking news to them. It's not like they're going to look at your crappy little list of blog comments & old directories and say "Well Penguin nailed this spammer, but now that he's admitted to link spamming, let's go after his wife and children". In my case, I have sites that lost EVERY SINGLE keyword. They can't kill me twice, so for those sites, I've got nothing to lose. I'll disavow every fucking link to those sites and start over clean.