McCain's campaign, meanwhile, launched an ad Thursday that sharply criticizes Obama's tax policies.

CNN: McCain, Obama ad wars heat up

Despite the worsening economy, online ad spending rose sharply in the second quarter, according to a report released today by IgnitionOne.

FORBES: Google and Facebook Lead Strong Q2 Online Ad Spending

In contrast, Pandora shares fell nearly 20% in after-hours trading on Monday, after the company beat third quarter earnings estimates, but cut its full year guidance sharply as a result of content costs and ad market headwinds.

FORBES: Why Pandora Missed a Beat as SiriusXM Surged

For the second time in six months, eMarketer has revised its revenue estimates for the social messenging service sharply upward, citing rising demand for the kind of native and mobile ad inventory it offers and a continuing extension of its reach.

FORBES: Connect