twice, including once in a petrol station (although this was in the ice/snow and we slid into one of the islands and the tyre went bang! - luckily with a renault 5 no need to waste time with a jack, one person could physically lift up the rear quarter of the car enough to swap the wheels over.)
on my own cars only twice
once was on my old trans am come back from playing golf to find a flat
and the other time was on my discovery in teh middle of the woods just after i got stuck in a puddle well say puddle was stuck up to the headlights in water lol
got towed out to find i got a punture when i was trying to spin my way out
Christmas day last year when my mum hit a pothole in my Focus an smashed the alloy. It's going in again for repair on Tuesday with suspected steering rack problem.
I've only had to change a wheel 3 times. Most of the time I get to pump the tyre up and limp to a tyre place. Screws are the killer, these go down too quickly.