"It's D-Day for the broadcast networks. They've been living on borrowed time for the better part of two decades, thanks to advertisers willing to toss in more cash each year even as ratings slowly trended ever lower. But with the economy in a tailspin — and the Big Three auto manufacturers, some of TV's best advertisers, near ruin — the biz may finally have to pull the emergency cord.

Already smarting from a writers strike-impacted season, the networks haven't had much more to celebrate this fall. Collectively, the Big Five (including the CW) are down 13% among adults 18-49 vs. last year. How low can they go? And at what point can the networks no longer monetize ratings that don't look much better than cable?"