When making a new post (not a reply) if subject field is left blank it is impossible to make a post, you need to hit back button and fill the subject in. The annoying bit is that whatever you've written in the Post field gets lost. So you're there writing and writing then hit continue but forgot to enter the subject - it's all gone as soon as you hit back on your browser (tested on firefox).
This is probably something that needs to be looked into. Temporary solution: edit 'newpost' template and put value="No Subject" in the Subject <input> element. When you will be making new post next time, the subject field will not be empty if you forget.
