One of the most common issues with Google Calendar sync is exceeding your quota. People with alot of history in their calendar (for instance, trying to sync your calendar at work) will run into this problem often, and often times without even realizing it. This issue can occur without your knowledge and you may be missing seemingly random reoccurring events. Fortunately, Google provides logs of what Google Calendar Sync does. If you browse here: (Windows XP): C:\Documents and Settings\%username%\Local Settings\Application Data\Google\Google Calendar Sync\logs (Windows 7/Vista): C:\Users\%username%\AppData\Local\Google\Google Calendar Sync\logs you will see that there is a log file for every attempt made to sync your calendar online. Errors in the log file are identified as "SEVERE" and often provide a decent description of what the problem is. If you've exceeded your quota, you cannot guarantee that Google Calendar Sync will update your online calendar. A quick workaround for people with large calendars is to do the following: (These instructions are related to any version of Outlook and may be duplicated in any email client supporting the .ical calendar filetype). If you have already uploaded some appointments to your Google Calendar but some are missing, clear out your Google Calendar (if you are starting fresh, skip to step #2). Open your Google Calendar from a computer. Click Settings then the Calendars tab. Delete any calendar listed under My Calendars. From Outlook, click on the File Menu and select Save As... Click on the More Options button at the bottom of the window. Change the date range to "Whole Calendar". Change detail to Full Detail. If there is an Advanced section, expand that and make sure that "include attachments..." is NOT checked. Click OK. You will receive a confirmation window. Confirm your selection. Choose the Desktop as a place to save the file to and click Save. From Google Calendar, select Import Calendar and browse to the file that you just saved. Click Import and wait for the calendar to finish importing. This process will help to alleviate the data intensity that is associated with synchronizing a large history with Google and will prevent quota issues. Another common issue is the inability to resolve calendar attendees with a contact list. Since Google has to resolve the addresses against its own contact list, alot of contacts will produce "SEVERE" errors in the log file. I have yet to see this cause a problem with my sync, but people have reported missing appointments because of this issue, so be aware. One more thing, if you create a text file in the logs folder named level.txt and put the word "VERBOSE" in the file, you will get a "VERBOSE" level of logging that will detail each and every action that Google Calendar Sync is doing.