Chris at Performancing has a great top ten list on how to get more comments to your blog. My favorite is #6:
Resist the urge to make your posts too complete if you want to receive community input. That’s one of the great things about top ten lists, you have to stop at 10! Don’t put everything into the post, especially if you know your audience has certain expertise they are bursting to share!
Full article: 10 Tips for Attracting More Comments