Dave,
I'm still of the belief that it's just a different wave of spam and part of the seasonal increase in volumes.
Having said that, I suspect that
Postini will sort this out for you when it's rolled to the live platform.
As a short term measure try setting up an IMAP folder on your account and move all the unmarked stuff into it. If you don't mind PM'ing me your username, the name of the mailbox, and the name of the folder then I can see if I can make sure your mails go through the training filter.
Rgds,