FORTUNE -- Facebook Home (fb), the social-media site's attempt to put itself more at the center of people's digital lives, has been downloaded more than 500,000 (but less than a million) times after being released nearly two weeks ago. That either sounds like a lot or not very many at all, depending on your perspective. It's an essentially opaque number -- or at best, a datapoint that is meaningless without context.
Facebook Home is a layer that lies on top of the Android operating system. It's not an app, and it's not an OS. Wired has decided to give it the unfortunate descriptor "apperating system." Others just call it a "launcher." The fact that nobody can agree on what to call it might be an indication of the challenges it faces.
Facebook supposedly has more than a billion users, so 500,000-1 million downloads of Home doesn't seem like very many in that context. As The Next Web pointed out on Monday, Instagram's app was downloaded a million times in the 24 hours after it was made available to Android users last year. (It had been out on Apple's iPhone (aapl) before.) Facebook's own Android app (not Home -- the regular app) has been downloaded somewhere between 100 million and 500 million times. Google Play offers only ranges, not precise numbers of downloads.
On the other hand, Home is available on only a few Android devices so far. With more distribution channels, it might pick up.
It seems likely that many of the people who have downloaded Home have done so mainly out of curiosity, with no real intent of keeping it as their mobile hub. The user ratings seem to bear this out: It averages just a 2.2 out of 5 stars, and more than half of the people who have rated it have given it just one star. This number might not mean all that much -- reviewers are a self-selected group, and in this case, people intent on being negative might be the ones most likely to rate the product.
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The core problem for Facebook is that while a lot of people use the social-media service, many have mixed feelings about it. They love interacting with family and friends, but Facebook itself -- with its changes to its interface and navigation and its sometimes confusing privacy policies -- is the object of widespread debate. It has succeeded in large part thanks to timing -- it came along just as MySpace was losing favor, and it managed to attract a critical mass of users who wanted social media but had few options.
If somehow somebody were able to build a superior social media site and migrate everybody there all at once, Facebook would be over. But of course, that can't happen. Meanwhile, teenagers seem to be abandoning Facebook, in favor of a whole bunch of different online destinations -- ones they can easily get to without Facebook's help. Facebook Home seems to be at least in part an attempt to forestall such migration. If Facebook can guide users to non-Facebook destinations, at least those users are on Facebook en route.
But nobody needs Facebook for that. Much like the "portals" of the dot-com boom—think Yahoo (yhoo) and AOL (aol) -- the company believes that people want one particular service to guide them through their online lives. But we know that they don't. They simply want to get to what they need quickly and easily. That's the job of an operating system, like iOS and Android. Or of a search engine, like Google (goog) or Bing (msft). If people want to be on Facebook, they need merely to tap on the Facebook app. If they want to be on Google Maps, they tap on that. From a user's perspective, navigating the Internet may not need to be a branded experience.