Here's a great summary of online ad spending by the presidential candidates except for the fact that it does not note how trivial thee levels of exposure is even for McCain who ran the most impressions.
Clinton, with under a million impressions, is spending perhaps a ten thousand total.
This low spend indicates that the online marketing people are very challenged with this new media. A spend of million dollars online would saturate the online world with the message because you don't need much targeting for a prez campaign.
Maybe they are holding back for strategic reasons but I'm guessing that they just don't get it. Big firms continue to dominate the "thinking" about how to run online campaigns, and big firms consistently have their clients waste money on foolish and stylish high CPM image based advertising rather than dramtically cheaper and more strategic pay per click and cheap image campaigns. There is a huge amount of inventory available online for massive branding campaigns like a candidate needs.
Unlike other products where you need a lot of targeting, a candidate for national office generally wants to talk to *everybody*. Even kids can have an indirect impact on election politics.
Given the jaw dropping sums about to be spent, I think we'll see the smart candidates work a lot more with online though agency ignorance of online marketing strategy may prevail in this realm.