Every day is something like April Fools' Day at the University of California Berkeley joke recommendation site, dubbed Jester.

Now on Version 4.0, the site tosses visitors a handful of jokes to rate on a scale of "less funny" to "more funny." It then recommends jokes based on the user's taste (or lack thereof), dynamically making recommendations based on the user's most recent ratings.

Jester's more than a joke jukebox though. Underlying it is a Berkeley-patented "collaborative filtering algorithm" dubbed Eigentaste, now on Version 5.0. The more people who use the system and rate jokes (4 million-plus ratings have been made so far, according to a recent story on the UC Berkeley Web site, the more data Berkeley researchers have to advance their understanding of recommendation systems, such as those used by Amazon.com and other Web sites.

"There are many applications for Eigentaste ... it can be used for recommending things where there is a large inventory like books, music, and movies, and can also be applied to recommend Web sites, restaurants or software utilities," says engineering professor Ken Goldberg, who got Jester off the ground 10 years ago and is now director of the Berkeley Center for New Media. "The key is that it separates the pattern analysis into offline and online components."

Among those other applications is Donation Dashboard, which helps people figure out an appropriate way to divvy up their charitable donations.

Goldberg (Tavi Nathanson and Ephrat Bitton are the other two listed on the Jester 4.0 team) says there has been a resurgence of corporate interest in licensing Eigentaste of late, though he declined to name names.

The first joke that Jester spit out at me was:

How many feminists does it take to screw in a light bulb?

Answer: That's not funny.

I won't tell you how I rated that, but I did ask Goldberg if he had any good IT jokes for me and he deflected the question by referring me to Jester. I didn't find much in the way of IT jokes, though I did run across a few science ones, such as this knee-slapper:

Two atoms are walking down the street when one atom says to the other, "Oh, my! I've lost an electron!"

The second atom says, "Are you sure?"

The first replies, "I'm positive!"

I thought I might have better luck asking Goldberg for his best April Fools' prank, either one played by him or on him.

"On April 1, when I was 6, my mother yelled that Martians had landed in our bathtub! She'd poured in green food coloring and it was out of character for my mother: When I ran in I was totally confused....but I never forgot that moment," Goldberg says.

Oh, and Jester itself was kind enough to serve me an April Fools' joke --- one of the popular Chuck Norris variety, no less -- just as I wrapped up this story:

Chuck Norris' calendar goes straight from March 31st to April 2nd; no one fools Chuck Norris.