Apple's .Mac online service lets you share photos and movies with your friends. It also lets you share your iCal calendar, Address Book, and Safari bookmarks between Macs. And .Mac provides backup service for all your documents, including purchased iTunes music.

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It's a good service, although there is one big problem: The maximum amount you can store on .Mac is 30 Gbytes. (30 Gbytes? What is this, 2002? Most people have well more than 30 Gbytes of photos, movies, iTunes, and other miscellaneous documents.)

Still, it's worth getting, for redundant backup. And the iCal, Address Book, and bookmark sharing are nice. But use some other backup service as your first line of defense against lost data in case of system failure.

.Mac's biggest strength is that everything is integrated into the operating system. The Web Gallery allows users to easily share movies and photos through iMovie or iPhoto. .Mac offers Web site hosting, and you can author your site with the desktop iWeb application. IMAP mail lets you access your mail from your mac.com address via a Web browser, Apple Mail, the iPhone, or any IMAP- or POP3-compliant mail client. .Mac Groups lets you coordinate activities with your family, friends, or workgroup using group e-mail, or a shared Web site and calendar. Sync synchronizes bookmarks, calendars, Keychain passwords, contacts, and more. iDisk provides file storage online, as well as document backup.

Pricing starts at $99.95 for a one-year subscription, which includes 10 Gbytes of combined e-mail and file storage, and 100 Gbytes of monthly data transfer.

If you need more space or less of a financial hit, there are plenty of alternatives. Google's Picasa and Yahoo's Flickr are great photo-sharing services, YouTube lets you share video, Mozy offers Mac online backup in beta, and of course there are plenty of Web mail services. But .Mac offers out-of-the-box integration with the Mac OS; you'd have to install third-party software to come close to that with other services.

.Mac would be wonderful if it offered unlimited storage, like other online storage services such as Amazon S3 and Mozy. But the current storage caps are a severe limitation on the service's attractiveness.