I've had it once, fortunately I was flying with another pilot, who heard "You have controlllllllll" as I shot towards the back of the aeroplane.
I was once asked as a certifying engineer to approve the design of an aeroplane which had a seat rail design substantially the same as the usual Cessnas. I refused to approve it until they'd added a small cheap mod to put a backup strap along the floor so that once the seat was latched, the pilot could simply tighten the strap up - so if the pins went, the seat was incapable of sliding backwards.
When I explained the Cessna history, and showed that the total parts on the aeroplane would cost about a fiver, the company were quite happy. To date, the aeroplane's never had a problem!
G