Hotmail/MSN won't automatically whitelist you after setting up the Sender-ID but it will surely be easier to spot the problem if you will want to track it up to exchanging emails with their support team. They have also a tool for self-support which I did not find it very useful but you may have a different result.
Anyway you should setup also DKIM, SPF and Domainkeys to be on the safe side with the rest , especially with yahoo! (domainkeys).
You may find here more info about setting up these : Postfix with DKIM, Domainkeys, SPf and Sender-ID http://www.tai.ro/2010/04/03/postfix-with-dkim-domainkeys-spf-and-sender-id/