I use them, too. 49 bucks one way, baby.
I flew SWA lat year on business, $99 both ways.
I've noticed that while Southwest typically advertises cheap fares, I often have a hard time locking in those "special fares" to the point that the standard (read: non-low cost) airlines are often cheaper.
Incidentally, I've also heard that one of the reasons that Southwest is making such a killing right now--as opposed to the other airlines--is that it hedged the price of fuel some years back. While that's certainly great business and foresight, it will be interesting to see if the profits remain stable when their fuel contracts expire.