Thanks for all your replies!
(1) "Those who subscribe to receive posts receive posts. Those who subscribe to comments receive comments."
In another browser, I went to my blog and clicked the Follow link at the bottom and subscribed with another email address I have. I received a confirmation and confirmed it. But I was not presented with a choice to receive posts and/or comments.
(2) "Your site stats page displays how many followers you have, who your followers are, as well as how many people are subscribed to post comments on your site"
In my test, the Follow popup said "Join 153 other followers." I just created by blog a couple of days ago, and have not received but a couple of notices that people are following me. Is it really possible that there are 153 people following my blog already?
I looked where you said, and it does say I have 153 followers: 3 wordpress.com blog followers, 52 Twitter followers and 98 FaceBook followers. The only ones I can see are the wordpress.com followers (2 - one person I don't know and me) and one email follower (the friend who accepted my invitation).
So the followers count is really just a total of my wordpress.com followers + my FaceBook friends count (since I connected to it) plus my Twitter followers count (since I connected to it), right?
It's not really people who are intentionally following my wordpress.com blog per se, right?
Since I found my friend/subscriber in the followers section, rather than the users section, what is the users section really for? Why, for example, is my friend who is now an email follower not listed as a follower in the users panel? Why isn't the wordpress.com follower listed there as a follower?
It's from there where invitations are sent. I would expect to see the followers there as well.
(3) "Don't forget that they can subscribe to RSS Feeds for posts, comments, categories, tags, etc. For example to subscribe to all posts the RSS feed is:
To subscribe to all comments made on your blog the RSS Feed URL is http://douglerner.wordpress.com/comments/feed"
Yeah, that's going to be the problem. It was confusing enough for my friend who is an experience programmer to figure out. I can't imagine how I'm going to get my current Posterous subscribers to figure this out - especially those who are quite elderly.