Question is, how many of those $9 fares are there? And you have to buy them by noon today. Plus, it's actually at least $18 since it HAS to be a round trip. But, not all flights are operated the same, BUT you can combine the fare with another segment. Which means, you can fly roundtrip, but you might be paying $9 to get there but $150 to get back. Oh, and don't forget to pre-pay your checked bags on-line. $19 for the first, $25 for the second EACH WAY. So, if you check one bag, you're up to at least $56. If you wait to pay for the bag at the airport, add $6 since it's more expensive to pay to check it at the ticket counter. Oh, and the passenger usage fee each way makes it $70. Segment tax each way makes it $77.20. Up to $18 per round trip in airport charges (aka landing fees) and the 9/11 security fee: $100.20.
Oh, and you have to be a "$9 fair club" member, with a fee of $39.95, making that $9 fare a grand total of $140.15 if you stay domestic. If you go international, the fees and taxes are on top of that as well.
Gotta read the fine print.
So, between the MUFF "diving" and the probability of people saying "No $9 left, be hey! $39 isn't bad either!" I'm gonna go with Marketing WIN.