If you are using an optin form with a submit button, do yourself a favor and change the name. In my experience, you should almost never use a button with the name “submit” on it or “subscribe” or “sign up” for that matter. This is because my experience shows me that people are more reluctant to join when you use those words. Do something else, be different.
I think that if you use “Get instant access” or “Yes, I am ready!”. People will be more positive to sign up for whatever you are offering. Just take a look at one of my splash pages and you can see that I am not using submit or subscribe. I am not saying that this splash page is any good or not, I am only concentrating on the button.
I haven´t got any statistics to show how big the difference is between the ordinary submit / subscribe / sign up and more creative buttons, but I think that you should at least try it. You can find even better words for buttons than the ones I suggested.
… what sort of button would you click on? That´s how you should think. Maybe something like, “instant access to millions” 🙂