Update 5:25 p.m. PT with other sync tools.
Online calendars are great but the problem is you tend to have one at work and a separate personal one. Now you can see events in both calendars at once, at least if you are using Google Calendar and Microsoft Outlook.
Google released Google Calendar Sync on Wednesday, which allows you to sync up those two calendars.
The tool gives you control over which direction you want the synchronization to go as well as how often you want it to happen.
The software was easy to install, and I was able to see the Outlook items in my Google Calendar but not the other way around for some reason. Oh well. Once I get this figured out it sure will be useful.
There are other Outlook calendar sync tools, but most aren't free. Jotlet announced two-synchronization with Outlook and its calendar last year. Another interesting one is Calgoo, a Java-based app that syncs online and offline calendars, including Google and Microsoft.