Sometimes the excerpts chosen for the digest don’t make a lot of sense. This can happen when a post starts with a couple of short paragraphs (usually a salutation and an introduction.) It can also happen when a post starts with "Hi 
". For these cases, increasing the character count in UserNotificationHelper#first_paragraph_from could make it more likely that the excerpt has some substance.
I noticed a lot of posts in the BoingBoing digest are just a title and a “[Read the post]” link. It may be that that’s the way they want it. If it isn’t, and those posts are just being picked up by Post#best_post, it could help to add a word_count constraint to that method. Something like: posts.where("word_count > 7").order('score desc').limit(1).first