Results
Email marketing, if done correctly, provides a great traffic boost to anybody's site and business. Below are graphs produced with different site statistic packages. See if you can guess when the email marketing was sent for each one.
Here we can see two distinct points where email marketing has been used. Also, notice the sustained increase from the first boost for two days after the mail shot.

Here, it is easy to see when the email marketing campaign was sent.

This site's traffic is more dependant on the weekday, but we still see a very clear boost of twice as much traffic, compared to a usual good mid-week day.

Here we can see smaller mail shots followed by a larger one towards the end of the month.

This site receives very little traffic on an average day. The results of the email marketing, with the large peak of traffic at the end of the month makes the rest of the month's traffic look totally insignificant.