Wall Street Journal quotes research by marketing-technology company Responsys Inc on the Emails being sent by Retailers. Some great facts in there:

1. In 2011, the nation's top 100 retailers by e-commerce revenue sent recipients an average of 177 emails apiece, up 87% from 2007
2. Neiman Marcus Group Inc. sent each recipient more than 500 emails apiece in 2011 which is 30% more than what they sent in 2007.
3. The rates at which recipients open retail emails and click on links have declined, in the first six months of 2007, consumers opened 19% of the retail emails they received and clicked through to the website 3.9% of the time. By the first half of 2011, those numbers shrank to 12.5% and 2.8%, respectively.
4. Sending fewer emails have paid off for some retailers, Nicole Miller has seen the rate at which customers "unsubscribe"—or request to stop receiving emails—drop, and the percentage of recipients who open the emails has grown from 15% to 40%, according to Andrea Marron, director of digital strategy at the company. Meanwhile, the percentage of online sales that began with an email has grown to 17% from 10%.
5. Loyalty program members tend to open more emails then general subscribers. Members of the rewards program typically open more than 30% of the Gamestop emails they get, compared with less than 10% for general subscribers.

Read more: Stores Smarten Up Amid Spam Flood

Gone are the days when online shoppers would wait for 2 seconds for your website to load, now they will switch at the blink of an eye.

For Impatient Web Users, an Eye Blink Is Just Too Long to Wait

People will visit a Web site less often if it is slower than a close competitor by more than 250 milliseconds (a millisecond is a thousandth of a second).

“Two hundred fifty milliseconds, either slower or faster, is close to the magic number now for competitive advantage on the Web,” said Harry Shum, a computer scientist and speed specialist at Microsoft.

The performance of Web sites varies, and so do user expectations. A person will be more patient waiting for a video clip to load than for a search result. And Web sites constantly face trade-offs between visual richness and snappy response times. As entertainment and news sites, like The New York Times Web site, offer more video clips and interactive graphics, that can slow things down.

But speed matters in every context, research shows. Four out of five online users will click away if a video stalls while loading.