While I agree with everything bhartzer says, I know from experience that Google very often fail to take detectable steps against specific spammers, even after repeated reports from multiple complainants.

It is a frustrating manifestation of Murphy's law that many of your competitors will get away with blatant SE spamming, while you will no doubt incur penalties for the smallest accidental transgression. Grrr...

Some SEs say that they don't always take direct action against reported SE spammers because of the sheer number of offenders and complaints. They say that they use the information from complaints to improve algorithms instead.