Online sales growth has slowed significantly in recent years, though still outstripping that of traditional retail stores. In 2002, online retail sales, excluding travel, were up 43.8 percent, to $53.5 billion, according to trade group This year, online sales are predicted to increase 21.5 percent, compared with 2005, to $138 billion.

Still, targeting existing online shoppers can be lucrative for retailers. A report this month by Forrester Research showed about 10 percent of online shoppers had spent $500 or more during the past three months. These heavy Web shoppers have an average household income of $91,296, and more than half have a college degree, Forrester said.

Getting them to spend more on the Web is important, but Erika Serow, a partner at management consulting firm Bain & Co., said online retailers also need to focus on convenience, easy navigation and checkout, and providing detailed information about merchandise. By contrast, new shoppers are most concerned that their transactions are secure.

"You don't need to fancy up the Web experience," Serow said. "You just need to make sure it is as consistent and pleasant as the in-store experience."

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