I've used faregeek several times and have saved hundreds to thousands of dollars each time. I've never had a bad experience, it's not like using a regular online TA, it's a regular TA that books your reservation then tickets it in the office the next day. If they have issues with your credit card, etc, they'd call you on the phone. Anyway, my experience with FG has been fine and saved tons of money. I've also had positive experiences with vayama (though less recently). I haven't used the other two sites - I see a lot of negative reviews for airfare.com (whereas for faregeek i see one person posting to a lot of sites), though, and i've never used ticketpilot. All of the consolidator sites are useful for really good deals on int'l flights, often when there's nothing on the airline site; in general, I'd always rather buy directly, but many times the financial difference is far too great.