I have found a way that allows me to be quite efficient in grading blog posts. I use a laptop to view the blog posts and my iPad along with a Google form to complete the rubric. View the images below to see iPad screen shots of the process. In the screen shots I am using the Google app.
*note: I created the Google form on a laptop prior to using it on an iPad.
*note: I used Skitch to create the screen shots below - great app!