Google does a great job filtering spam in gmail. I'm not sure how important the "report spam" button is in this, but it is certainly somewhat satisfying to press it. Where is the will to do the same thing for their search results? I'd like to see a similar button in Chrome (for starters) for social rating of spammy websites. Other comments have noted that this would shift the goal posts to gaming the social rating system. Maybe one solution to this would be to weight ratings by reputation. So Google detects that you are someone who rates spammy web sites highly, and devalues the rating you have applied to all other sites.