I haven't yet but I have heard great reviews about them on the Las Vegas boards I visit. My friend at work is using them this year to fly to Vegas and we are going to use them next year to fly to LA and them back from Vegas.
I go on www.lasvegastalk.com The guys there are very friendly and will answer lots of questions as many of them are locals. They do talk a lot about gambling strategies though which I don't understand!! lol