I can confirm this as well. The 3.3.x patch to our 3.3.4 forum installs (all of them) caused them to completely halt during any topic post operations. IPB: Please send out a NEW announcement email to all clients when you FIX the 3.3.x security update. Thanks.
We ran the "Resynchronize Topics" on our forums, and now the database for ipbtopics has "Guest" and "guest" for "last_poster_name" and "seo_last_name" respectively. The "last_poster_id" is still correct, however it seems the resync tool is simply broken when pulling and updating data for the topics table.