Good call. Digg watchers and insiders speak in hushed tones about "the algorithm" and how hopefully Digg will tweak it to great effect.
On Reddit you get an open source system with a one-stop appliance for any would-be submitters. The comment sorting algorithm is explained in a blog post by the xkcd guy (http://blog.reddit.com/2009/10/reddits-new-comment-sorting-s...).
On the flip side, reddit may not be profitable.