Where did you expect to enter messages? When the groupblog plugin is activated it will create a blog for that group. You can then visit the backend of that blog and make posts like you normally do with WP. Note that users are actually added to the blog when they visit an actual blog post of that group.
Currently we have not implemented posting blog posts from the group yet, but it is on our to-do list, at least for quick text only posts. In this way it would behave much like creating forum topics.
We are retooling the plugin after BP 1.1 gets out, so look out for some changes (mostly under the hood) in October/November.
My expectations were a blog would be created (met) and when people clicked on the “blog” item in the group, they would be taken to a separate blog and people would be able to post to the blog.
