I've had colleagues experience this on Southwest too. They were on the early flight out of...New Orleans...to Houston, and it was struck by a passenger shortage mechanical failure. Everyone was re-booked onto the next flight, but my colleagues were an hour late to our meeting.
This was definitely not the case yesterday. The flight was actually overbooked, and I'm certain they'd have rather sent the plane empty than have to deal with the yelling and screaming they had to endure for 7 hours. People were simply animals. It was actually quite shocking, as I've experienced airplane delays before and never did people behave like that. It probably didn't help that most people were returning from the annual weeklong drinking convention.
As for SWA and empty planes, my experience (and info from a maintenance mechanic friend of mine) is that SWA generally doesn't have the "luxury" to do that. They don't have spare planes, everyone is scheduled every day (unless its out of service for scheduled maintenance), and they have to get that plane to the next city for the next flight. I was once on a flight on SWA where I was one of three passengers.
I much prefer flying Southwest over United (the internet isn't big enough for me to list the things I prefer over flying United), but SWA are starting to lose their mojo. No one would ever book a trip on United, or most other major airlines, with the thin tolerances for delay that many people will risk with Southwest, because Southwest has always been so simple and reliable. If that faith starts to slip: (1) it'll be nigh on impossible to regain; and (b) they will lose some of their advantage over other airlines, and thus customers to them.
SWA still has advantages in cost, and as such will always be the airline for vacationers and kids going to visit grandma. But it will definitely affect the business travelers. SWA has worked hard in the last few years to attract and take better care of their business travelers, but if their tight scheduling turns into too many delays, they'll certainly lose share in that market.
