Would have to say very much so and ended the trend of bigger and bigger food and beverage options. I remember there being a coffee chain that was competing with Starbucks at the time that introduced a full 44oz frappucino-type drink, and convenience stores starting to introduce 52oz sodas. Seemed like the sky was the limit back then but all those super-sized options disappeared within about a year after Super Size Me.
I just flipped through the introduction of a GIMP book that the authors hoped 3.0 would be out so they could cover it but ultimately based the book on 2.6 due to delays. It’s copyright 2012, apparently something (didn’t) happen.