Southwest Rapid Rewards - Flight 511 5/24 MDW?

Curious if anyone knows the situation of this flight number today. I didn't quite clearly hear it the few times it was mentioned but had a 2 hour delay in Denver and MDW was mentioned amongst it all. Thanks!

Don't know the reason, but according to the info at flightstats.com (http://www.flightstats.com/go/FlightStatus/flightStatusByFlight.do?airline=WN&flightNumber=511&departureDate=2012-05-24&utm_source=airlineInformationAndStatus&utm_medium=cpc&utm_campaign=co-op), all legs after BNA-MDW at 6:00am were significantly delayed (90+ minutes).