http://zqktlwk5ilgohy63eyrptyb4mc76bunfmxcnstkmveyjnskxkpq3b5yd.onion/wiki/Anonymous_Communications
All of the anonymity stuff is covered in this HOWTO, of course, but they also give some legal information that may be of use to you. Note Blogging in general is seeing increased mixing with social network software. As such, you need to be especially careful about your Social Network and your audience of your blog. If most of the people who end up viewing and posting to your "anonymous" blog are your friends, family and coworkers, you don't really have any anonymity.