I’ve been playing around with the latest version of Elgg, which is 1.6.1 but it became a little too difficult to keep up with conversations on group discussions and blogs, so I wrote a plugin to do it, BlogWatch. When you install it, you get a Subscribe button on a blog page as well as on a group discussion page:
If the post or topic already has subscribers, you’ll see a Show subscribers button whether you’re subscribed or not:
and if you are subscribing to anything, there will be a new button on your profile status page allowing you to keep track of your subscriptions:
If the post or topic is deleted, all subscriptions are also deleted. Whenever a new comment or reply is added to a post or topic, you’ll get a message using your preferred medium, which is normally email.
You can download the plugin from its page on my github site, or from its Elgg page.