We have been using an rss feed for a long time..
http://virtualtrials.com/feed.xml
We have hundreds of people subscribed. Our feed basically describes changes to our website, which is about brain tumor treatments. So whenever we add an article or clinical trial, it is automatically added to our feed. It not only keeps our members informed, but it leads them back to our website much more often than they would return without the feed. (We also send out email newsletters, but not as often as the feed is updated, so the people who really need the information fast use the feed!)
Someone asked how to construct it.. we also use dreamweaver - and cold fusion. All scripts that enable us to add content to the website automatically add an entry into a database that the feed uses to update itself.
Creating the feed itself is simple for your web programmer. It is a very easy syntax.