User-reported spam in gmail is actually very efficacious. Aside from the logic gmail applies to your inbox specifically, Google's current violation threshold for those reports is .03%. Beyond that, those reports start to pull down sender IP and domain reputation, which impacts overall deliverablity to anyone's gmail inbox.
This is why I am quick to report spam, even if they are a "legitimate" business. Utility company / paypal / whoever wants to send me spam? I sincerely hope they are impeded from sending email to anybody.
