Google is set today to open Google Drive, a service to store files online and share them among various computing devices that turns out to be a lot more important than you might think.

Why? Two reasons:

First, Google’s service goes well beyond rivals because of integration with Google Docs, Google+, Gmail, and other services.

Second, beyond a basic free level, ordinary consumers will pay to use Google Drive — not much, but enough to make them into customers, not just users of an advertising-subsidized service. That’s a pretty big philosophical shift for Google.

What is Google Drive?

Google Drive, at its core, looks a lot like Dropbox: you install software on a device running Windows, Mac OS X, Android, and “in coming weeks,” iOS. That device gets a special Google Drive folder that synchronizes its files with a mirror stored online.

If you copy or save a new file to the folder, or if you upload one to the Google Drive site online, the technology automatically replicates it at all other Google Drive locations. On an Android tablet, though, you’ll need a network connection to actually see the files behind the file names.

“You can take all your data, regardless of which device you’re on, and make it seamlessly available to you,” said Sundar Pichai, senior vice president of Google’s Chrome and Apps projects. “We want you to think of this as the center of your Google apps experience.”

It’s very useful, as Dropbox users can attest. I use Dropbox often, for example saving a PDF of my airplane boarding pass and a subway map when I’m at my computer, then pulling them up on my mobile phone when I need them even if I’m in a foreign country without my usual wireless service.

But Google outdoes Dropbox by giving you 5GB of capacity for free, 25GB for $2.49 a month, or 100GB for $4.99 a month — via Google Wallet, of course. (Or, if you’re feeling like pushing the envelope, there are other tiers including $50 a month for 1TB and $800 a month for 16TB.) Dropbox’s free tier ends at 2GB (unless you cajole your friends into joining with your referral code), then jumps to $9.99 monthly for 50GB or $19.99 monthly for 100GB.

That’s more expensive than the existing Google prices for overflow storage space at Picasa and Google Docs, which can be had for $50 a year for 200GB compared to $210 for Google Drive. That’s because Google expects much more active use, with data being sent to and from multiple devices frequently. “This is something we expect people to use with high utilization a lot,” Pichai said.