Microsoft’s Outlook blog contains a fairly dire warning about problems experienced by users of the plugin:
When a Google Apps user installs the sync plugin for Outlook, the plugin modifies a registry key which disables Windows Desktop Search from indexing and providing search functionality for all Outlook data, not just the Outlook data being synchronized from GMail. Because Outlook search relies upon the indexing performed by Windows Desktop Search, Outlook search functions are broken as a result. It is also important to note that uninstalling the plugin may not fix the issue.
It’s likely this problem will get fixed in short order, but it doesn’t sound like racing to install the plugin right now is a good idea. Hit the Microsoft post for further details and a registry fix if you have installed the software, though this doesn’t sound foolproof either.
Google Apps Sync Disables Outlook Search [Microsoft Office Outlook Team Blog]