Dropbox said 500 million customers have signed up for its cloud-based file storage-and-sharing service, highlighting its popularity as it battles Box and a number of other rivals. Dropbox claimed 400 million users in June 2015.

There’ s no question that Dropbox is nearly ubiquitous: It’s installed on nearly a half a dozen machines in my household alone. But then again, I rarely use it and to my recollection have never paid for it.

And therein lies the problem with claims like this in a world where profitability (or at least a path to profitability) has become increasingly important for high-flying VC-fueled startups. In the past, companies like Dropbox could point to growth metrics—unpaid users or eyeballs— as predictors of success.

Not so much any more as some big institutional investors including Fidelity Investments and have taken to revaluing startups, including Dropbox, on their own rosters.

So it’s worth noting what Dropbox does not say in its post. It does not indicate, for example, how many of the 500 million sign-ons use the paid service versus the free version (for storing up to 2GB of data.) The problem with free trial and freemium models is that it’s extremely hard to convert users (is it wrong to call them freeloaders?) to paying customers.

 

Watch How Dropbox Is Wooing Businesses

Another issue: There’s a ton of competition. Google goog Drive, Microsoft msft OneDrive, Box box all offer similar capabilities. And Google and Microsoft, at least, have other cash-cow businesses to subsidize file-sharing and storage if needed.

Dropbox: Businesses love us too.

In November, Dropbox said that 150,000 organizations use its paid Dropbox for Business version, and Monday’s blog post name checks News Corp. nws , Absolut, Dentsu, and GIW Industries as customers.

Nor does Dropbox really note how active these users are although it did say that since the company was founded in 2007, users have created 3.3 billion Dropbox “connections,” meaning they used the service to share, annotate, or otherwise collaborate on files. It also said that sort of activity soared 51% last year from the year before.

Still there’s that nagging question of who, if anyone, is paying for all that activity.

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Given that the nine-year-old San Francisco-based company has raised north of $600 million in capital it is extremely well funded. But it’s also unclear what sort of exit it has in this environment.