There is a pretty popular four page thread taking place at Search Engine Watch for the past week. To be honest, I have stayed away from it for the most part. The thread is named How Long Does It Take For Search Engines To Remove Spam Sites?
But that question is really not answered. The discussion goes into the ethics of reporting spam. Some relate it to snitching on friends or colleagues. Some say instead of reporting the spam, work on making your site better. Some say, they report spam because they felt mislead, while others report spam as part of the SEO package they offer clients.
I personally like the question, "How Long Does It Take For Search Engines To Remove Spam Sites?"
It depends of course. I have reported spam here before, and it took less than a couple of hours to be pulled. Point being... reporting spam via the spam reporting tool would probably take a much longer time then reporting spam in a very public setting, such as a forum or a blog. Why? Because it is embarrassing for the search engines to have such blatant spam in the SERPs and to then have members discuss it in a public setting. That is why WebmasterWorld, one of the most popular and active discussion forums on the Web, is so against link drops. Just one of the many reasons, actually.