As more and more people begin using Chrome extension to report spam, Google've now allocated appropriate resources to the spam reports that are mostly likely to be useful.
"Spam reports are prioritized by looking at how much visibility a potentially spammy site has in our search results, in order to help us focus on high-impact sites in a timely manner. For instance, we're likely to prioritize the investigation of a site that regularly ranks on the first or second page over that of a site that only gets a few search impressions per month. A spam report for a page that is almost never seen by users is less likely to be reviewed compared to higher-impact pages or sites. We generally use spam reports to help improve our algorithms so that we can not only recognize and handle this particular site, but also cover any similar sites. In a few cases, we may additionally choose to immediately remove or otherwise take action on a site," explains Google.
More Info: Submit spam reports