Here's a despicable statistic, 66 to 88% of all e-mail is spam, and attachments-based spam is on the rise. Security firms have the figures for the various measures of spam floating around.
This ItWeb article talks about Greeting Card-based spam along with Symantec's statistics regarding image and attachment-based spam. These mails contain a link to a downloader program that installs a Trojan on the system. This article at USA Today further details the types of spam that are rampant today.
While spammers seek more intricate techniques to fox spam filters, this PC World article quotes David Salbego, UNIX and operations manager of computing and information systems with Argonne National Laboratory, a division of the Department of Energy (DOE) operated out of the University of Chicago. "Ultimately, filtering spam at the content level will become less and less effective. A better way to control spam, in my opinion, is by considering the source of the message -- the IP address of the mail server attempting to deliver the message."
Newer and better techniques are indeed a necessity at these times when Social Networking and other collaborating media are making information mining all that easier for the dedicated hacker. There are many effective spam filters, but perfection in this area has been a far call so far. What is your experience with the various spam filters?