Spanning Sync’s eponymous utility is designed to perform just one task easily and efficiently: syncing event information between iCal ( ) on your Mac and the free Google Calendar ( ) service. Although it does the job adequately, it fails to sync some important data—and if you use it to keep multiple users’ iCal calendars in sync, even more complications arise.

Google recently added CalDAV support to Google Calendar. So if you’re using the Leopard version of iCal, you can now connect directly to a Google Calendar, with full read-write capabilities on both sides. However, at the moment, the combination of iCal and Google Calendar alone has several problems—including an inability to sync properly with iPhones, lack of support for non-Roman characters, and limited technical support—so Spanning Sync still serves a useful role.

The user interface of Spanning Sync (a pane added to the System Preferences application) is simplicity itself. After entering your Google ID and password, you select a checkbox to turn the service on, choose a syncing frequency from a pop-up menu, and select the iCal calendars you want to sync. For each calendar, you pick one of your existing Google calendars as its online mate. Spanning Sync then merges the information in the two calendars and keeps them up to date as you modify the data on either one. (In this respect, Spanning Sync is much easier to comprehend than BusySync’s publish-and-subscribe model, which can’t directly merge existing calendars.)

The briefest possible interval between automatic syncs is ten minutes. This could result in missing information—for example, if you make a change in iCal and then, five minutes later, put your Mac to sleep and head off to work, the new event information may not appear in Google Calendar. I therefore frequently found myself syncing manually, and although that required just one click, it became a hassle over time.

When Spanning Sync copies data from iCal to Google Calendar, it can upload only the information Google supports. Because Google Calendar has no concept of to-do items or attachments, those items won’t be available online. As a result, if you decide to keep iCal on multiple Macs (or multiple users on a single Mac) in sync by connecting to a given shared Google Calendar with Spanning Sync, be aware that some data won’t sync among users.

Worse, though, is the fact that alarms and meeting attendees—which Google Calendar does support—don’t get synchronized either. (Any event you create in iCal will show up in Google Calendar with the default reminders for that calendar.) Competitor BusySync does synchronize that data, with a few qualifications. On the plus side, using Google Calendar as a conduit for syncing iCal at least guarantees that syncing will continue to work if any of the computers go offline.

Macworld’s buying advice

Prior to the introduction of MobileMe ( ), Spanning Sync met an important need, making it possible to edit your iCal calendars from any location with a Web browser. However, if that’s all you need to do, MobileMe now makes that easier and more convenient than using Google Calendar—assuming you don’t mind the $99-per-year fee. (You can, by the way, use both services together if you want.) If you prefer to stick with Google (or if you need access to a Google Calendar someone else has shared), Spanning Sync gives you most of the same calendar syncing and editing capabilities, at a significantly lower cost. But it’s not ideal for keeping multiple copies of iCal in sync with one another because so many kinds of data don’t survive the round-trip to Google; for that task, BusySync is a much better choice. Meanwhile, Google Calendar’s new CalDAV support means people with very basic syncing needs can link iCal and Google Calendar directly, leaving out the middleman entirely.

Joe Kissell is the senior editor of TidBits and the author of numerous e-books about OS X.