I've updated the blog header a bit to have the logo take you to the home page and have a Blog link just for the blog.
Heh, it's not actually part of the "main site"; we're using Posterous for the blog, but I'm really happy you think it is part of it -- means my CSS hacks have worked. :)
Yes the subdomain is different, but they both share the same domain (that's what I meant by site) and both have to deal with the same thing--your company. Seems like they should as close to one another in look and feel (and navigation) as possible.
Wouldn't it be simpler and much more straightforward to just add a blog link to both your blog and your main site, make your blog look like your main site and make the logo link to your main site. After all, isn't your blog part of your main site?
Also, when you click on your profile link on the right of your blog you get a posterous profile page. Seems like that should link to the about page as well.