Hi Chetan,
Agree Outlook IIS logs will log a user authenticating to CRM. What I do is I filter per folder. e.g. when a user synchs with Outlook it only request's certain URL's and example would be the /XrmServices/ folder.
Parsing the logs with sawmill allows me to easily separate folder paths and user logons so I can identify what users are really doing, it still cumbersome but I don't have a great alternative.
Another example using IIS logs is I can identify which users are editing records.
Hope this helps