Nearly half - 47 percent - of internet users who reported researching products online during the 2005 holiday season bought those products offline, at a bricks-and-mortar store, by phone, or some other offline channel, according to a new "Post-Holiday Online Shopping Study" sponsored by iProspect and conducted by JupiterResearch. As a result, search engine marketers may be underreporting campaign results by as much as half and therefore losing budget dollars to other channels, iProspect says.

Also, although 62 percent of internet shoppers used general search engines (such as Google and Yahoo) when researching products online, only 26 percent used shopping-specific search engines (such as Froogle and Yahoo Shopping), according to the study.

Moreover, 63 percent conducted research at merchants' sites, and 30 percent reported doing so on manufacturers' sites.