I did once think that I wasn't getting notification of updates, but now I
think it was just Outlook being slow to push them to the server -- or user
error on my part. It does seem to be working just fine.
<soap:Body>
<SyncFolderItems xmlns="http://schemas.microsoft.com/exchange/services/2006/messages">
<ItemShape>
- <t:BaseShape>AllProperties</t:BaseShape>
+ <t:BaseShape>IdOnly</t:BaseShape>
</ItemShape>
<SyncFolderId>
<t:DistinguishedFolderId Id="calendar"/>