I just posted a mini case study on how to create an a/b test for follow on emails. It's for more advanced users of the system. Even if you aren't you should take a look as it might give you some ideas on programs you can run.
First I want to thank the client for letting us use screenshots of her program. Here's what she's doing. She sent out a cyber monday promotion on Tuesday, 11/24 to her entire list. Rather than send out just one follow-on email, she wanted to test whether Friday would do better than Monday. So, she's using distribution groups to "stage" the follow on emails - half on Friday and half on Monday. You can check out the mini case study on how we did this on our online help system. Click here.
I'll update this post with some results as we get them over the next few days.