Creating custom Calendar Providers for Outlook 2003

I just came across this article on MSDN about creating custom calendar providers for Outlook 2003.  It’s an older article (May 2004) but this is the first I’ve seen it.  Outlook 2003 has the capability of using a web service exposed by Sharepoint to pull down a list of events and display them (read only) on a calendar.  The idea is that people would use this to attach to a group calendar in Sharepoint and be able to see the dates, etc. from within their Outlook 2003 Calendars, right along side their own calendar.  The article takes this a step further by providing a means to be have a custom data provider, rather than using Sharepoint.  This way people can hit a service that exposes the data for the read only Calendar events.  Unlike the requirements of Sharepoint (such as Windows 2003, Sharepoint itself, etc.) this only requires a web service somewhere (hosted under any web server) that has the correct interface defined and returns the data in the correct format. 

The author provides some examples of his class by including a group of implementations of his class, such as a RSS Calendar Provider, an Event Log Calendar provider, a Messenger Conversation Calendar Provider, and a few more.  He is also using a Plug-in Model to allow for the ability to provide additional implementations.  All in all a cool article and some neat technology.

EDIT: Oh, and if you want to use a web service to add items to this list then check out this other blog entry.