Not me - it runs just fine on regular (87 octane) fuel and I see no reason to pay extra. But when I go to those crazy states where they sell 85 octane I do spring for the 87.
In the U.S. there is no advantage for Premium per se (for Prius). The main thing you might want is TopTierGas.com as that has extra detergent additives in all grades including Regular. In the U.S. we have two basic types of gasoline, EPA Reformulated Gasoline and so-called Conventional Gasoline. Florida is in the Conventional Gasoline category. What that probably means is that there could be a little more freedom in formulation, and so there could be a little more variation between brands and between grades. So if you were trying to set the world record Prius miles per tank, which we don't hear much about these days (but back in the Gen2 era that was a common contest) you might with experimentation find some stations had a little higher MPG formulation in Premium, in Conventional Gasoline areas only, but there is no guarantee. Canada, all non-U.S. countries, are a little different story...we have E10 mandate all grades.
I walked into a British Columbia (Canada) Shell station this afternoon (yes, I've got the bug): Regular is 10% (ethanol), midgrade is 5%, and highest is 0%.
