What you see is probably just spammers adapting to the new situation that almost everyone's using filters nowadays. If you look at the code of the e-mails, you'll probably notice that most of the words aren't written even close to natural English. Any word that could be caught by a filter is just a resemblance of the real world. You as a human will still understand the message, the computer doesn't, sadly.
Right now, I'd look into SpamSieve (search versiontracker.com) or creating your own whitelist-based rules in Mail.app (i.e. create rules for the mails you WANT to receive) like I have done. I don't meet more than five people a week who're going to regularly send me important E-Mails (and neither do you...), so it's not that difficult to stay up to date. Once a week I scan the 'white-list-failed'-folder, where everything else goes that Mail.app's spamfilter didn't filter. There I'll find new contacts that aren't in the white list and mailing lists stuff that has a different sender address than the last time...
