I've noticed that the web server has been running slowly today.

Anyway I think I've found the problem. One of my old blogs sites is currently being spammed. Currently there are 3.3 million comments in the database!

EDIT: Problem fixed:

mysql> delete from comments WHERE id > 556;

Query OK, 3305122 rows affected (2 min 21.45 sec)

EDIT2: The spam has been coming from caravan.ru a Russian ISP (who's logo is very similar to optus' old one...).