Hi erinz,
Thanks for visiting our site. Yes, I think Friday and Saturday are generally good days to visit Epcot.
If you click on the "Crowd Blog" link in the lower, right corner of our home page, you'll see the actual wait time data from the Magic Kingdom we used to come up with our estimates for that park.
If we look at the worst-case waits for the Magic Kingdom's headliner attractions, Saturdays tend to fall in the bottom half of the rankings. Sundays, Mondays, Thursdays, and Fridays are all worse, IIRC. And I think our crowd blog and "Best Days" calendar does a good job of explaining how we came up with these data.
Regarding the "Saturdays are busier" theory, I think it's an urban legend that just won't die. I've never seen any actual data from the parks that support the idea, and the wait times from the Magic Kingdom show it doesn't appear to be true.
Finally, don't forget that your day-of-week choice is about five times less important than getting to the park early, and having a good touring plan. So I wouldn't stress about day of week too much.
Thanks again for visiting our site!
Len Testa