Hi Colin
I consider any email SPAM that is unsolicited coming from anyone I don't know, no matter what the subject may be. I think that the ultimate spam filter would probably be the easiest to implement. I maintain an address book that contains the email addresses of those that I correspond with as I'm sure everyone does. Why not use this address book to filter the email and only allow mail from someone in your address book to be delivered to your inbox. All others could be routed to a folder as "suspected junk mail" that you could peruse and add addresses to your address book if desired to prevent future filtering. This junk folder could be automatically purged after x number of days to prevent it from becoming unmanageable.

I believe that this would be the simplest, most effective filter that could be devised.

Key word filters are difficult to maintain and many times filter out real mail. Maintaining a list of addresses that you won't accept (blacklisted addresses) simply does not work since there is almost an infinite number of addresses that send out spam and spammers simply change addresses, cloak their address, or hijack legimatate addresses and continue to sent their crap.