I agree with the line-up issues. I find that if I hit the Costco (Etobicoke) on my way to work in the morning I never wait more than a minute or two, even when the price is really high--all about what time you go. Been doing it since they opened, no gas issues yet.
For our old Hyundai regular gas was typically 4 to 6 cents cheaper, still some savings in the long run but no way worth a line-up. Now that I am running premium (Saab Turbo) the saving is even bigger. Usually in the 10 to 15 cents a litre range (there have been times where the premium there is only a cent or more than regular everywhere else)! Still not worth a line-up, so I pick my time.
I find the price difference to be pretty constant, what I find really odd in a way is why are all the SUVs line up when reg gas is in the 1.40 range but there are no lineups in the 1.20 range? If it is always say ~5 cents a litre cheaper regardless of price. The SUV holds say 100 litres, you save as much as $5.
Now if it is 5 cents cheaper than 1.20 you save $5, if it is 5 cents cheaper than 1.40... you save $5. It is still $5. Somehow $5 is worth a 45 minute wait when gas is 1.40 but not at 1.20.... I know it is about the total price, but $5 is $5!