Junk mail can be a serious drain on personal productivity. I figured I'd mention what I use as another piece of information about dealing with the nuisance. I have a long-standing Yahoo Mail account that I picked up after leaving the university world. I've since moved on to accounts on my cable internet provider and my own domain names, but I've kept the Yahoo partially as a backup and to keep good vibes going with the YahooGroups. It's also smart to use a separate address for mailing lists than for your traditional personal / business mail.
Due to some of this strategy and some luck, the Yahoo account gets the most spam, and how fortunate that their Bulk Mail Filter automatically grabs all the junk before it comes down to my machine. I go into that account every week or so, and easily clean out several hundred spam a day. I don't even bother to check for false positives because I have told my contacts to find me elsewhere.
On my home machine, I have set up Popfile for Bayesian spam filtering of spam (and also categorizing other mail), and I use the Outclass interface within Outlook, rather than the separate engine that runs in the background. I like that it is trainable, and the amount of spam that makes it through to my home machine is only about 20-40 a day, so it is still possible to browse the spam folder for false positives. At this point, I only get a false positive a few times a month, though there are the one-a-day false negatives (spam not classified as such). A touch of a button, and Popfile will catch anything similar.
I also like Popfile/Outclass for its ability to file messages into other folder, based on Bayesian classification, just like the spam. This means I can train it to recognize some fairly specific mail without needing to create new Rules. (Training is handled by either clicking a button or telling it to reclassify to one of a dozen categories.) I'll agree with David Weinberger that it isn't the most friendly or well-documented tool in the world. Now that it has been running for several months, I don't really think about it.
My webhost has SpamAssassin on its servers, but I was not happy with its overly-aggressive filtering. And this particular setup was not designed to let me tweak the settings. If spam becomes a major problem through my host accounts, I will have to turn SpamAssassin back on and deal with checking mail on the host from time to time.