I recently upgraded my blog to BlogEngine.Net and since then the comments stopped working. Seeing as I'm more busy than Obama right now, I never really stopped to properly troubleshoot it. Recently I took up the challenge and thanks to someone else having the same issue, my blog is now fixed and users can add comments to my posts. So please, comment away!
If you're looking for the solution for your own blog, see http://blogengine.codeplex.com/Thread/View.aspx?ThreadId=59277.