Yes I delete about 1 spam a week on the DME forums currently. I also have an email notification for all new messages posted on these forums, so it makes one more spam in my mailbox
The viagra one is now gone.
For all the spam I had, they always create a user account before posting, it is not guest posting.
When I will open registrations on the new site, there will also be a visual confirmation (a
captcha), and users won't be able to post without logging in. Although there are methods to workaround even these, it still dramatically limits the amount of spam.
However, for the discussion forums here, I agree with beowuuf: the amount of spam we get is not yet enough to ban guest posts.