The Interactive Advertising Bureau released figures showing online ad spending up 33 percent in 2004 over the previous year. Consumer advertising made up just under half of all ads, distantly followed by computers (18 percent), financial services (17 percent), healthcare (6 percent) and telecom (4 percent).

Spending amounted to $9.6 billion, according to the study, which used publicly traded firms' SEC filings as representative of the industry generally - a practice that has proven inaccurate in the past.

CPM ads accounted for 42 percent of advertising. Click-based pricing rose to 41 percent of spending. A hybrid of both methods was used about 17 percent of the time.