The only time I had a train all to myself was on American Eagle backwards last year during ERT. It was awesome, and quiet too, as the blue side was way behind the red side.
Absolutely:
Universal Studios Orlando & IOA
Busch Gardens Tampa Bay
Sea World Orlando
Fun Spot America
Probably:
Holiday World
WDW
Maybe:
Parque Diversiones Costa Rica
Six Flags Great America +1
Great Escape -1
Great Escape - 8
Six Flags America - 8
Six Flags Discovery Kingdom - 13
Six Flags Fiesta Texas -14
Six Flags Great Adventure - 15
Six Flags Great America - 18
Six Flags Mexico - 9
Six Flags New England - 10
Six Flags Over Georgia-12
Six Flags Over Texas - 12
Six Flags St. Louis - 10
I think they're very useful! There'll be times when I can't browse the forums when I'm busy, and those emails will keep me up to date with what's happening.
SFGAm +1
Great Escape -1
Great Escape - 7
La Ronde - 10
Six Flags America - 10
Six Flags Discovery Kingdom - 10
Six Flags Fiesta Texas -11
Six Flags Great Adventure - 10
Six Flags Great America - 13
Six Flags Magic Mountain - 8
Six Flags Mexico - 10
Six Flags New England - 10
Six Flags Over Georgia - 10
Six Flags Over Texas - 11
Six Flags St.Louis - 10