I've actually been wondering about this for a long time. I mean, given the fact that we are basically turning our food into charcoal to some extent, it seems like there has to be a link to carcinogens there somewhere.
The bottom line, according to the article:
So we know that PAHs and HCAs exist, and that they could potentially cause cancer—but let’s step back and consider this from all angles. First, the studies that prove them to be carcinogens were conducted on mice. The jury’s still out as to whether they’re harmful to humans. And besides: The amounts of PAHs and HCAs ingested in these laboratory studies were extremely high: We’re talking the equivalent of thousands of times more than an average person would consume.
A little prudence is worthwhile here, too, in light of the fact that it isn’t just grilling that causes carcinogens—essentially, cooking meat at a high temperature through any method (smoking and frying are the next biggest culprits; boiling and roasting aren’t as big offenders) has the same effect.