I have been thinking of this concept myself for a admin system I am developing. I think that a rss feed would be very handy but havn't been able to figure out how to make it private. Think I read somewhere about a way to put password on a feed, but some of the big rss readers does not support it yet (for example Google Reader).
One of the commenters to Ayende's post gave me a tip worth checking out. Unfortunatly it only works in Outlook / IE.
If you want to make RSS feeds private the easiest way (that works with Outlook at least) is to enable HTTP Basic Authentication and visit the RSS feed with IE to input credentials and check the option to save them. Then Outlook will transparently use those credentials to update the feed.