I went through the unnatural link thing from a competitor who had stupidly thought he could bad link our site. We got the message, and with just some investigating all the backlinks (I used the 75 free trial on Moz) to export every link and check out what was going on. I hadn't paid attention to backlinks before since I'd rather write articles.
I looked into the Google disavow and it just didn't make a lot of sense of how much good it would do so I contact webmasters on the link I saw were crap (make sure to use Gmail for this since they're watching) and did the reconsideration request. Two days later they sent another e-mail showing examples of the bad backlinks. These were on those crappy forum profiles of sh*t sites. I sent a few more e-mails to webmasters and responded to G very thoroughly pointing out that so many of the backlinks were done is a very short amount of time plus our site is very reputable so that didn't hurt it.
Within days, the penalty was revoked and the competitor got slapped real hard by G. To all those thinking that doing a negative campaign is easier than actual work...big G can track you down since most have no idea of what they're doing in the first place.
I would really use the disavow as a last alternative as there's no time limit on how long it will take to have any effect. If G sees that you're trying to fix a problem, they can work with you surprisingly.