Fixed it by:
mysql> OPTIMIZE TABLE hintlastnview;
mysql> REPLACE INTO hintlastnview (userid, itemid) SELECT ownerid, itemid FROM log WHERE year=2001 AND month=3 and day>=26;
It's down to 2/3rds index space capacity now, but I'm going to have to watch it. That limit should really be higher. I'll have to do more reading on the topic.
all posts now show up again, assuming the year/month/date was set correctly on them.