I've been doing this longer than many people here I think - although not recently due to injury.
- I cleaned the lens contacts of two cameras with eclipse / alcohol. Both failed during a wedding ceremony. I figured out why, rubbed the contacts a bit, and one came around. I didn't miss anything critical.
- One camera failed as the bride walked up the aisle. Other camera was out of arms reach.
Other close calls:
- Flash is connected to battery pack in pocket. Put camera down, walk away, everything falls to the floor (maybe twice)
- Put camera at feet, it rolled down a hill. Fortunately it was a Nikon D700 and it was unscathed.
- Put a camera on root of car, it fell off. Again, no damage.
- Dropped camera and lens onto thick carpet. Ruined the lens 24-70 F2.8 lens, cost $2K to have the entire internals replaced
- Put brand new 7D camera on tripod incorrectly, fell off, scratched the heck of out of it and it didn't work right
My insurance premiums started going up.
For weddings I tend to take three or four cameras, four flashes, studio flashes, multiple stands and cables, more triggers than I need, etc. I don't trust any equipment because everything fails sooner or later.