Dropbox will announce a number of milestones on Monday morning, we’ve learned. The file backup and sharing service was founded in 2007 by Drew Houston and Arash Ferdowsi.

It was in one of the early Y Combinator classes, now has 25 million users and 200 million files are “saved” daily, and more than 1 million every five minutes.

That’s impressive growth from the 4 million users the company had a year ago (they had two million in late 2009). Dropbox enables people to sync files and media across platforms and devices, in order to have them available from any location. The service also allows people to easily and quickly share files with others. Dropbox provides users with 2 GB of space for free, and they can pay for more.

People use dropbox for personal storage, file syncing between machines, and group collaboration on projects. They have desktop software for the usual OSs, and mobile access, that makes things run smoothly.

They are much more tight lipped on revenue and profitability, though. Guesses range all over the place, but the company is certainly efficient with bandwidth and storage. They likely only upload unique files. Common files, like songs and movies, aren’t re-uploaded repeatedly.

Whatever their revenue, the company is on a roll and will likely be getting a lot more attention in the near future. Perhaps even a large “DST-style” secondary round with liquidity for founders and perhaps investors. And this could be an IPO not too long down the road, too. Personally I’ve found the service to be increasingly useful as I use multiple machines. Efficient and easy cloud storage, along with the usual web services like email, make that fairly easy. Just a few years ago, not so much.

Our first coverage of Dropbox, at a YCombinator demo day, is here. They’ve raised just $7.2 million in funding from Sequoia Capital, Accel Partners and others.

We did a particularly entertaining TechCrunch Cribs tour of their office a couple of months ago.

My favorite Dropbox story though, and you can ask Drew this if you see him in person, is the time I found his unlocked iPhone sitting alone at a dinner table in Hawaii while he was off socializing a few feet away. So I did what anyone would have done. I set a password on the phone and put it back where I found it.