I like how Seller Tools has saved me time! Before, I never posted things to Twitter, Facebook, or Flickr, because I just didn't have the extra time! Since using Seller Tools, I have seen traffic to my store double, if not triple!
I like the keyword tool, It really puts things in perspective. I love the ability to see what is the most popular in my shop via views and purchases. The sort function is awesome! I just clicked on the analytics reporting page for the first time today and it seems like there is a lot of meaty information there!