EMail notification to act as modified list-serve??

[dermreview]

I would like visitors to my site to be able to "monitor" a thread, and receive updates via their e-mail -- even if they have not contributed to the thread.

I would also like to allow visitors the option to receive updates every time there is a new post to a sub forum, or forum.

It does not seem that vBulletin has this capability. Has anyone been able to do something like this??

Would you use an RSS feed??? The only problem is that this is a "general" feed, and not forum or thread specific.

Would you use an outside program like watchthatpage.com?? (Id prefer not)

Any thoughts are most appreciated!