Unlike separate search tools, such as Google Desktop, Lookout's quicker to access because it becomes part of Outlook's toolbar. Besides e-mail, the tool adds attachments, PDF contents, and folders on an IMAP server into its index.
Lookout also searches inside appointments and contacts (and you'll probably discover new connections between message topics and contacts). It works with all current versions of Outlook.
Note:Unfortunately, as of February, 2007, Lookout is no longer available or supported. It has been replaced by Windows Live Toolbar and Windows Desktop Search, which provide Search beyond just Outlook, according to a Microsoft spokesperson.