From what I understand, you could use excerpts to do what you want but then you would have to write (or cut and paste) and excerpt everytime you wrote an entry. I think this solution:
http://manalang.com/archives/2004/06/20/wordpress-plugin-condensed-content-for-date-and-category-archives
is much more elegant and straightforward.
I just figured out the problem here since I just had it. The problem is the “user_nicename” field apparently isn’t getting filled when users register themselves. This is what is used in the URL for this and thus since it is missing, your URL has nothing for the author. If you look at the link it’ll have a double slash (//) at the end of the URL. The user_nicename goes in between those. If you fix that for each user, you’ll be set. Although you have a lot of users so that may be an issue for you.
