Despite signs of an impending letdown in consumer spending, eMarketer forecasts that online sales for the fourth quarter will be $26.2 billion, up 21.9% over last year ? and shoppers shifting their purchases from offline to online will drive much of the gain.

Competition is going to be intense. Last year, rivalry among online retailers competing for "wallet share" led to aggressive promotions. Even though the effect of offers such as free shipping on long-term customer loyalty is uncertain look for more of the same this year.