Nope. Nada. Nothing. In years past, like 3-4 years ago, I would put Star-tron or Seafoam in my tank, supposedly to keep my engine running smoothly, if I wasn't going through my tank of boat gas very fast. But none of those treatments seemed to make a difference. If my engine was carbon-free and had decent plugs in it, it ran great, and if it was fouled, the gas treatments didn't help: new plug time. Since I have switched to exclusively synthetic oil, my plugs last a lot longer without fouling, and I use no treatments other than Sta-bil for winter storage. Use 87 octane with 10% ethanol exclusively. I don't think there's a guy in our bass club (20 boats) who uses gas treatments during the year, Evinrude or Mercury or Yamaha.
I treat every tank of gas with the Mercury products. Unfortunately there is no non-ethanol gas even remotely close to me... I combat this by trying to figure out how much gas I will use on a particular trip and do my best to use it and always put fresh gas in it from a busy gas station by my house.
It also is a great excuse with the wife "I NEED to run my boat and get the gas out of it before it gets to old and destroys my motor!"
I run real gasoline and run fuel stabilizer at an operational dose. The reason being fishing the Mississippi you never know what its going to do, boat might set most of the summer because of high water. I also use Amsoil HP Marine synthetic oil.