DropboxI’ve always been a big fan and committed user of Dropbox. Over the last couple years the handy file-sync app has gotten me out of many scrapes—when I need to access six-month-old interview notes when I’m out of town, it’s always a thrill to find them in my Dropbox. Along with my sit/stand desk, my Livescribe pen, and my MacBook Air, Dropbox is one of the few genuinely delightful tools I use regularly, and I’m constantly recommending it to friends and family.

And yet I’m extremely skeptical about Dropbox’s business prospects, and totally puzzled by the high hopes that otherwise smart people have pinned on its success. Dropbox is a great little file-syncing app, and founder Drew Houston and crew are already making some nice money out of it. But is it a $40 billion company? I doubt it. And when I hear folks like Benchmark’s Bill Gurley suggesting that it might be, and calling Dropbox “a major disruption,” I wonder if they’ve simply been blinded by the thrill of using an obviously well-crafted utility.

Gurley argues that in a multi-platform world—where we’ll all be carrying more devices that are possibly running a variety of OSes—we’ll clamor for some kind of easy, invisible, automatic way to keep our stuff synced between gadgets.

He’s right about that. We will need something to organize our lives between gadgets. The trouble is, it will be difficult to make a perfect gadget-syncing service that is also a great standalone business. There are two reasons for this. First, the perfect syncing service needs to do more than simply store files. Second, the perfect syncing service should be unlimited and free, or as close to it as possible. Dropbox will have a hard time doing the first of these for technical reasons, and if it does the second, it won’t be a very good business.

In its current form, Dropbox is great at syncing stuff that I’ve saved to my filesystem, but there’s a lot more to device syncing than just what I’ve stored in data files. When I switch from my desktop to laptop to my phone to my tablet, I would really like my device’s “state” to follow me, not just my files.

Right now, I happen to be traveling from the Bay Area to Seattle. When I left home, I was typing this article in a Word document on my Windows 7 desktop. The Word window occupied one half of one of my two huge desktop monitors. Splashed across the rest of the screens were several tab-filled Chrome windows, a few IM windows, and my text-based notepad.

When I later opened up my MacBook Air, I could access the Word file and my text notepad through Dropbox. But I had to make my computer do so. In a perfect syncing scenario, my laptop would know what I had been doing on my desktop and would offer to open up the right windows for me, preferably in the identical places on the screen—but Dropdox doesn’t do that. Worse, Dropbox can’t sync my Chrome and IM activity in any way. If I want to get the same tabs that I had on my desktop here on my laptop, I have to rely on Chrome’s own (fantastic) syncing feature. (There’s no way, as far as I know, to keep my IM windows synced between devices.)

I can think of many other things that would be great to keep synced between devices: Desktop icons and images, peripheral drivers (so that when I connect a camera to my work computer, my home computer recognizes it too), and application preferences (I like my Word documents set to 180 percent zoom).

I’m not the only one who’s been asking for this sort of thing. The Verge’s Joshua Topolsky has been yearning for a “continuous client” for years now, since back when he ran Engadget. But I’m hot holding my breath that we’ll see such super syncing anytime soon. Syncing the state of devices rather than just your files presents many difficult conceptual problems: What does it mean to sync windows between two gadgets that might have different windowing paradigms (say an iPad, which runs everything full screen, and your Mac)? What happens when you rely on two different apps to do the same tasks on different devices—for example, how would you sync tabs between Chrome or IE on your Windows desktop and Mobile Safari on your iPad?

Someday, someone will figure out how to make this sort of thing work well, but I suspect it will most likely be one of the companies that makes a major operating system: Either Apple, Microsoft, or Google. Each of these firms has a file-storage and/or syncing solution that it’s pushing, and I expect that those efforts—iCloud, Skydrive, Google’s Chrome syncing and perhaps the mythical Gdrive—will gradually incorporate more and more of the features I’m looking for.

Dropbox is probably working to build many of these features as well. But as third-party app, it’s just not in a very good technical position to do so. In order to sync programs and window states, Dropbox would need access to some of the deeper parts of my various gadgets’ OSes. This is easy for some operating systems and impossible with others—including iOS and probably Amazon’s Kindle Fire. Apple could easily build a way to sync the current browser tabs between my Mac and my iPhone, so that I can switch from reading Pando on my couch to reading it on the train. Dropbox will need to go through incredible hacks to achieve the same functionality, and it probably won’t manage to do so even then.

In fact, even now, as just a simple file-syncing app, Dropbox is frequently stymied by OS- and application-level problems. It won’t sync Microsoft Office files until you exit the application you’re using—if you forget to close your Word file on your home computer, it won’t be in your Dropbox at work. That’s not Dropbox’s fault—it’s Office that locks files that you’re using. But it highlights what I’m talking about: There’s a lot going on your computer, but Dropbox only has control over a small part of it.

You might argue that I’m making too many demands of Dropbox. So what if it doesn’t satisfy all the features I want—won’t people still pay for it if it keeps getting incrementally better as a file-syncing service? Maybe, but remember that online storage is a commodity. Dropbox makes money by charging people for increased storage space. But the price of storage keeps plummeting. It’s tending toward free. With all the competition it faces from firms with huge data centers, Dropbox isn’t going to be able to get people to keep paying $10 a month for 50 GB of space for many more years to come. It needs to add extra capabilities, too.

In 2009, Steve Jobs wanted to pay more than a hundred million dollars for Dropbox. As Houston later told Forbes’ Victoria Barret, when he politely turned down his hero’s offer, Jobs declared that Dropbox was a feature, not a product. Jobs was right: To do what we all want it to do, syncing has to be baked in to all the gadgets we use today. OS companies are warming to that notion—and they don’t need Dropbox to do it.