According to Computer World, Linux sales are "thriving." They say they wouldn't have kept it going if it wasn't working well, but they won't release any figures, saying figures don't really matter.
Seeing as Dell hasn't done any marketing whatsoever for this, this is fantastic. I think it shows that there is a big enough user base who are willing to pay for the service of having it pre-setup. Sure, many of could do it ourselves, but when you can ditch the Microsoft tax and skip to the best part of setting up your system—perfecting your personal settings—, why not? The thing I like about this is that they're a big name. They're kind of pressuring the other big players, and that's great. Of course, there are other companies which go Linux-only, like ZaReason, System76, and Emperor Linux, but none of them have physical walk-in stores. ZaReason is aiming to change that in the Bay Area, but I know I ended up with a Gateway (yeah, yeah) because at the time my mom refused to pay if we couldn't see it in a real, live store. Dell's in-kiosk displays may not run Linux, but they're still the same hardware, so getting a feel for how sturdily-constructed it is is still possible.