Peer-to-peer computing, or P2P, raises the hackles of copyright enforcers. And no wonder: File-sharing services such as Kazaa use the technology to link participating PCs in an informal and always-changing network, one that lets people swap MP3s and other files without centralized servers and services that could more easily be found and shut down.

But as with so many Internet technologies, P2P is only now revealing its true complexity. And it turns out that solving one of life's major headaches is both easy and legal using these same methods. Just look at BeInSync (www.beinsync.com), which lets you set up your own private P2P network.

Many of us use multiple machines, and often spread our work between computers at home and in the office. So BeInSync, based in Tel Aviv, Israel, decided to create a way for such machines to stay synchronized.

E-mail, contact information or Web favorites: You name it, BeInSync can ensure that when you change it on one desktop, your other computers will reflect the changes.

I like BeInSync because it saves time. Sure, there are various file-synchronization programs out there, but most home users want these tasks to operate behind the scenes. They'd like to set up the software and forget it's there.

Using P2P means BeInSync can do this, keeping files current automatically. You can change the network to add co-workers and define what you want them to see. Remember, it's P2P, which means this system never puts your files on third-party servers, but remains only on the machines you've authorized to work with your information.

Moreover, your data is readily searchable from the BeInSync client, and the software uses strong encryption that keeps unauthorized users from accessing your network. We'll see how well BeInSync is accepted in a world ever more concerned about privacy, but if this program's security is as tight as it looks, then using its powerful features could become a habit.

P2P is surfacing in many interesting applications, including a backup service now in beta testing called Magic Mirror (www.pensamos.com/mmb/). Here the pitch is to all of us who are too lax about backing up key data. Magic Mirror does it automatically, copying whatever files and folders you choose to other computers within your home or office.

Now I've got hundreds of gigabytes of spare storage among the three PCs in my house. Why not turn P2P loose so that each of these machines backs up the others? It's easy to select which folders need backup and which can be left alone. And the idea of making data backup routine and automatic is a winner, ensuring that hard-disk crashes or viral attacks won't cost you priceless work and time.

Magic Mirror is still in its testing stages, so you may want to wait until version 1 comes out. When it does, the software will be free. Until then, ponder other P2P services like the intriguing BitTorrent (bittorrent.com), which is designed as a cheap and effective distribution network. Instead of distributing through central servers whatever program or publication you're offering, BitTorrent spreads the downloads across users' PCs.

We may get to the point one day when expensive collections of servers seem like an antediluvian approach to computing. This is happening because high-bandwidth connections are becoming more common, while disk storage is growing at an ever-faster clip. P2P, then, may have become the sworn enemy of the recording industry, but the methods behind it could become mainstream, a process that has already begun and now seems to be accelerating.