Guest posting usually means that you leave the blog post for around 24 hours on the homepage, with the full text and links, so that the guest blogger gets some link juice.
Your blogposts appear on the homepage only as excerpts --> the backlinks do not appear on the pr6 page, but on a weak pr 0 page.
You have so many posters, that your website is similar to an article directory.
You get a better deal by posting on ezine articles - super powerful pr 6, than posting on an expired pr 6 domain with weak backlinks.
Anyway, congratulations for your strategy, i am a little sad that there are so many noobs here who fall for this, but on the other hand it's good there are still some smart people on bhw.
Good luck with the project.