The thumbs down should be given for inappropriate blog posts, i.e. stuff which isn't related to maemo, the internet tablets, etc., and also for posts which are on-topic, but are rubbish for whatever reason (don't make sense, etc.)

I can't remember how the karma metric is calculated for blog posts (and it has probably changed too), and specifically for the negative impact of "thumbs down", however I proposed that only the blog post tally is affected by the negative thumbs down, so it doesn't impact on the karma gained from the rest of your work on/for the tablets.