For Aidan and anyone else who has trouble commenting on Blogger: the simplest method is to ignore all the 'openID' etc. options in the drop-down menu, and arrow straight down to 'Name/URL' or, if you prefer, Anonymous. There is no need to enter a URL, unless you have a website or blog. Simply input your name and leave the URL space blank.
We hope to migrate PE to a more comment-friendly platform in the near future, but hopefully the above will help in the meantime.