eMarketer forecasts that in the US in 2010:
Over 57% of online ad spending will come through the top four portals.
Ad revenues at the top four mega sites will rise to over $13.5 billion.
Ad revenues at the four portals will rise by 3.7%—but with great diversity among them.
Yahoo! will get nearly $1.3 billion in display advertising revenues.
Google will get over $8.1 billion in paid search advertising revenues.
Average ad revenues per unique visitor will range from $8.33 to $52.50 at the top four sites.