I have been playing with SQL Server 2008 recently. There are many new features which SQL Server 2008 have. One of the interesting addition to SQL Server 2008 is system table field which records when SQL Server was started. This field has data type as datetime that is why it is precise to 3 milisecond.
Note : This will not work with SQL Server 2005 or earlier version. This works with SQL Server 2008 only.
Reference : Pinal Dave (http://blog.SQLAuthority.com)