This makes me think ... I bet this and the very slow posting/replying are all related. I'd bet my bottom dollar that this is all related to the SEO functionality added recently ... not to mention that on a high traffic server these types of things can grind you to a halt if not setup right :/
Again if you want a hand with this stuff ehmax just shout and I'd be happy to lend a hand where I can.
No I haven't seen this again, it might have been isolated to that time but I suspect that this may be related to the issues the other folks are having with it taking forver posting new threads and replies. It sounds like it may be potential mod_rewrite problems (which is what is likely being used for the SEO addons).