I'm really surprised at how much of a difference this made, so I wanted to share this with all of you. My web site's feed originally only showed every post up to the "<!--more-->" a.k.a. "continue reading this article" point (which was usually after the first paragraph). I didn't really like the way this looked, so I removed the "<!--more-->" from all of my posts and allowed my feed to show the entire post.
Since then, my subscriber count has nearly doubled. And I haven't written a post in almost a week! 
I'm new to the feeds, so I initially assumed people only cared about having a feed notify them when a web site posts something new. But now I see it's more than that; subscribers want to know of new posts
and be able to read it without having to visit the site.