Yes. And since I moved to Manassas I swear every restaurant is slowly getting worse. Several places should probably take the day off and flush their lines. Maybe check the mix ratio.
Fountain pop at fast food places is usually slightly watered down so they can sell more for the same price, so it tends to not be as "strong" as a can or bottle. But yeah I do find there is a difference, fast food pop is more "watery" and less fizzy. Oddly if I'm really thirsty I actually do prefer the fast food pop for some reason.
Of course. In the local bottling plant thousands of drinks are made every day to the exact same specifications (within tolerance). Every fountain seems to be set up slightly differently in terms of the mix, amount of carbonation, etc.
My wife claims that the quality of a restaurant's fountain drinks is generally indicative of their overall quality. So far I have few reasons to doubt that claim.
That whole system is (AFAIK) maintained by Coke. I worked for the big two McD and BK and coke always sent their local guy to come in and calibrate the setup. This wasn't done that often.
One thing to note is that water varies from location to location so in example since the water in Waco Texas tastes just fucking horrible, so does the fountain soda. Or as the wackadoo people there would call it "fountain coke" even when they were drinking Sprite.
There's also a clear difference in flavor from Can->Bottle->Fountain. There's something about the Can that is just irresistible.