Track days are about as much fun as you can have fully clothed. I've driven at Bruntingthorpe, Elvington, Llandow, North Weald and my all time favourite Anglesey (several times). All the track days I've been on have been well organised and I've only seen one 'incident' which was due to an idiot in a BMW arsing about and planting his car in the pit wall.
As far as binning it I think I've spun my car on the majority of track days but never sustained damage, at Bruntingthorpe I think I lost it at near enough 60 mph and spun 3 times accross the grass. That was the fastest I ever lost it, most of the time you're not really going quick enough to travel too farr off the track unless you're being a prat.
I've not heard a single good report of the JapFest track experience at Castle Coombe, too many idiots on the track.