Henry Blodget and Silicon Alley insider have good commentary on how Google / Yahoo / AOL and Microsoft are grabbing ad spend away from the likes of Time Warner, Viacom, CBS, NYT and other TV, Cable, Print and Radio outlets.
The online companies, in other words, picked up 7 percentage points of market share in a single year.
Traditional media executives--especially in the newspaper business--often blame their current woes on "the real estate market" or "cyclical weakness." Economic weakness may be exaggerating the downturn, but it's not the real problem. Whatever weakness is hitting the newspapers is also hitting Google.
These trends are secular, not cyclical: TV networks, radio networks, and newspaper companies won't suddenly wake up one morning and find themselves back in charge. Individual Internet companies may screw up (see Yahoo/AOL), but if they do, others will rise to take their place (Google).
They have a spreadsheet that spells it out in stark numerical detail.