http://okcupid.com

A matchmaking site, different from match.com, Yahoo personals, etc., in these ways:

* It's completely free, even to send messages.

* The users write the questions.  The software watches how people use the questions, and rates the questions on that basis.  A question gets a high rating if users mark one or more of the answers as important for an ideal mate to choose ''and'' different people tend to value different answers (so it separates incompatible people and groups compatible people).  For example, one of the high-rated questions is, "Did mankind evolve from primates?"  Many people have a definite answer to that question that they want from a mate, and indeed different people answer it differently.  That's not a question that you're likely to see on one of the vanilla sites.

* You can answer as many or as few questions as you like.  The more you answer, the more data the system has to rate matches.

* Along with a user's profile, you can see which questions they consider important.  You can then click on those questions and answer them, bypassing the system's choice for the next question to give you.

* The users also write "tests": personality tests that categorize or rate people.  For example, in addition to MyersBriggs tests, one user has written a test to rate your skill with commonly confused English words, another has written a test to determine if you are a Nerd, Geek, or Dork, another has written a test to categorize your preferences in women's physical proportions, etc.

* The Famous OkCupid Test, written by the founders, categorizes your ''dating style.''  Their descriptions of 32 different dating styles are fascinating reading in and of themselves, and unflinchingly brutal.  If you're a "Manchild", maybe you don't want to go chasing a "Wild Rose".  Just seeing someone's dating style might be the most valuable four bits of information you can get for deciding whether to pursue a relationship.

* The software keeps on updating its statistics and matching information, based on every question that every user answers.  The site is running a huge empirical feedback loop.

* There is an overall feeling of intelligence about the web site.  They let the users use it however they like, to meet whoever they like, for whatever purposes they like.  They don't patrol the profiles for naughty words like some sort of chaperone.  To post new questions, a user must first answer 500 questions.  This simple measure greatly reduces the number of duplicate questions in the database.  The authors of the site are mathematicians, and have a page explaining the statistics that drive the site.  No hidden corporate malarkey, no bullshit.

* How nice! The site doesn't toss cookies at the casual visitor.

Some negatives:

* S-l-o-o-o-o-o-w.

* Crazy CSS causes each page to render in a jumpy, irritating way, at least on SafariBrowser.  It is so irritating that I just want to quit the site after a couple page views.

* My whole computer seems to slow down when I'm on this site.  JavaScript?