I've bought airline tickets twice from them. You're not as likely to get the amazing deals that you'll get on hotels or package vacations, but you can still find some good prices, especially if you're looking for tickets during a peak travel time.
Unlike Priceline, if they cannot find tickets that suit your needs, you are under no obligation to pay. They ask you to send alternative travel arrangements to make it more likely they can help you, but if you want you can pick the specific flight numbers on specific days (as long as they fit the parameters stated in the auction, which are frequently restrictive on travel days, travel dates, and locations). If they can't give you what you ask for, the auction is cancelled, no harm no foul.
The great thing about Skyauction is their pro-customer attitude. They don't require a secret minimum price the way Priceline, Hotwire, and other discounters do. If you win an auction for a price so low it's practically criminal, they don't tell you to go away, they are happy for you. They get their minimum price with the "service fees" they charge; beyond that, they're glad to give it to you for a dollar.
Can you tell I love Skyauction?