The only time I've stopped on a block on a coaster was on corkscrew at Alton Towers, but at the block section, the train is going at like 2 miles a year anyway so it wasn't bad. But we were stuck there for 30 minutes in what was at the time, the hottest day of the year and it wasn't so nice, but we did get passes to get straight on rides via the exit, rather than queueing, so it was well worth it IMO [:D][lol]
The worst stopping in general on a coaster though, that I've been on anyway, has to be the black hole at Alton Towers. When you have a 21 stone bloke sitting behind you in the seat, it BLOODY hurts at the brakes, I can tell you