Thule Fairing

I bought the Thule fairing, and it has done exactly what it said it would -- it completely took away the annoying whine from my roof-top rack. Not sure if it has added anything in terms of fuel efficiency, but I was mostly looking for blissful silence. The one thing that I would say is that it looks like it will install best if you have the standard square Thule bars. I have a less-common style of Thule bars called "t-slot aero bars". These bars are rounded-H-shaped, and the racks attach in the channels on top. The problem with that type of bar is that the fairing attachments then render that bar useless for then attaching anything else. The fairing attachment simply sticks up too high. I had to get a separate bar for the fairing and leave the two standard bars for my racks. It works fine that way, it was just a hassle and more unexpected cost. If you have questions about what I mean, just look at page 3 of the instructions, and you will get the idea.

The gas mileage stuff other reviewers claim is kind of a joke. If there were equipment sensitive enough for regular joes to measure their gas mileage that accurately, we'd have these same people sealing their windows shut for eternity, passengers & baggage weighed and gas tanks minimally filled.
That said, the noise is gone. It was previously most notable with the windows closed as it likely caused the chassis to hum.
I will say, though, that I suspect that Thule's instructions for installation have an error: It instructs installers to use one location on the mounts for outer brackets and another for the inboard brackets. They were numbered 1 and 2 on the sheets. I remember that in order for the fairing to fit properly, I had to use the exact opposite locations respectively.
Otherwise it is a worthwhile option to install.

I have a 2010 Mazda 3 with Thule Rapid Area bars. Before the fairing, I got an awful howling sound at speeds greater than 60 mph. I was concerned that I would hate driving my car after dropping several hundred on my rack so I got the fairing.I was skeptical that it would help any, but it totally got rid the howling. Now I can barely (if at all) hear the rack and I'm back to quite driving.Cons: Too easy to steal (no anti-theft). Too expensive for what you get (it's shiny and nice looking, but plastic!). Although it snaps onto the aero bars fine, I had to modify (cut slits into) the rubber strip that goes in the middle of the bar to accommodate the fairing clips.Overall, I'm happy I got the fairing.

This fine piece of plastic, similar to Yakima's but nicer looking, keeps your rack quiet whilst speeding down the interstate. Also a great spot for all you sticker freaks to sport stuff that you're not getting paid to sport. As for helping with gas mileage---now there's a master marketing tool, and that's all it is.
A bit of advice: If you want to keep your sticker displayer on your rack, replace the stock hardware with nylon locking nuts or if you have bucks to spare, buy the ten dollar security lock from Yak or Thule. It takes twenty one point six seconds for the casual thief to remove your fairing in the dark, no flashlight, no barking dog.

Roof racks rob you of gas milage, most folks who love the outdoors are also concerned with the overall state the of the world. Here is some simple math. My faring increase my gas milage by 1 mpg (from 19 t 20), at $60.00 and $3.00 gas the faring pays for it self after 7220 miles. Americans average about 15,000 miles per year, so the faring pays for it self after six months. Of course this is very simple math, it ignores several variables which are beyond my calculation here, but I think the general concept is sound.

Bought a 38 for the rack on my old VW in 01, and it is now still fully functional and still saving me gas money on my current Subaru Outback. Very easy to install and although its mostly plastic, I haven't had any issues with breaks or cracks - not even in the winter. It definitely will save you money; on my Subaru it saves me approx 1-2 mpg without my spacebox up top. When this one goes the way of the buffalo I will buy another, but will make it oversized.