I would also include the number of replies, although I must admit that I've never implemented such a system myself. Typically, the best articles have the most replies, and quite often, the most interesting content is the replies themselves.
http://reddit.com/info/1dk74/comments
My concern is when Karma has an impact in your ability to contribute.
The karma system is pretty interesting... there are definitely many variables to play with in calculating "karma," but the end goal should be largely the same -- measure a user's contribution to a community and also how trustworthy the user.
While I am not familiar with current systems, it does look possible to accumulate the same number of karma points by say, submitting a few very popular articles, or by submitting many less-popular articles. So are these two users treated equally when their scores are the same? If yes, then the system is ignoring some valuable information! If no, then karma becomes a rather meaningless measure.