Q: Is the guest post sent to moderation? How is it stored while the user registers?
I took a look at this tonight on a test site. The guest post is actually stored in a new table so it doesn't show up in any queues or anywhere else that a normal post would. If the guest registers an account then the post in the temp table is submitted as a normal new post would be so at that point it'd be subject to moderation & so on. If the guest does not create an account then the cron job will delete the post from the temp table after a set period of time.