GetUser()()() retrieves the user information from the data source and creates a MembershipUser object populated with the returned data. If you use one of the GetUser overloads that does not take a username parameter, GetUser returns the information for the current logged-on membership user. The current logged-on membership user is identified by the Name of the user in the current HttpContext.
You can also specify whether you want GetUser to update the last-activity date/time stamp for the user being retrieved using the userIsOnline parameter. Of the GetUser overloads that do not take a userIsOnline parameter, GetUser() implicitly updates the last-activity date/time stamp for the user. GetUser(System.String) and GetUser(System.Object) do not.