Prior to its release, Snakes On a Plane was being hailed for its genius marketing plan. The movie ultimately bombed. What was the main problem?
the studio's attempts at social networking were viewed as patronizing
the R rating made the movie less accessible to a wider audience
the movie was friggin' terrible, but not in a good way 
the marketing campaign ignored the core, niche audience
No matter how many leads a marketer generates, it's still critical that the advertiser be able to properly handle the lead and close the deal. Fair or unfair, advertisers judge their marketing partners on the overall rise in business...not just leads.
Snakes On a Plane missed the mark so badly that most people didn't blame the marketing. Unfortunately, most advertisers aren't willing to admit that they might be the reason your campaigns are failing to convert to new business. It's important that marketers go beyond simple lead generation and help advertisers respond to leads appropriately.