I'm really curious.
I think QS is probably more popular in communities like hacker news because there are a lot of people here that understand:
1. Computers think faster than you 2. Computers remember more than you 3. You can use the above to solve interesting problems.
Combine that with pervasive computing/surveillance and you enable yourself to remember arbitrary amounts of things and mine insights from them.
Empirically, it's probably a young person's thing, because people tend towards conservatism with age, and the technology required is going to be something young people are more comfortable with. But there are plenty of older people involved in QS.
Not yet. But they make calculations faster.
I use QS tools to define where some degree of normality is, so my simple monkey brain doesn't lie to me and I can see when I cross that line :).
I find this sort of thing especially helpful when trying new medications/treatments. It's nice to have a chart that I can look over to help give me a better idea about what's going on with my body. "Oh, ever since I started this new medication, I get headaches when I don't drink at least 4L of water."
There's no way that I'd be able to keep track of my day-to-day symptoms without writing them down; the days often blur together.
Oh, and doctors love it, too.
Left to my own devices I'll end up eating out for all 1-2 meals a day, only move from the bed to my car to my desk, forget what sunlight looks like, pull 12 hour days and 4 hour nights of sleep (or stumble into a 48 hour cycle), IM only my closest friend every few months, get suicidal and quit another job because nothing matters and the world is cruel.
For me at least, quantified self is not about trying to treat myself like a machine, it's about trying to remember not to.
The examples on the site include how many tweets you wrote (ok), tracks you listened to (erm... ok), checkins you had, and the max degrees Celsius for your location that day (what?).
In general, you optimize what you measure, but eventually it becomes a parody of itself.
But number of tweets, or number of checkins per day? Nah.. or maybe it's a play on something Oscar Wilde wrote.. "To live is the rarest thing in the world. Most people exist, that is all." Not that I mean to be snarky, I assume it's up to the user what stats to display and hopefully how to display them; but to get me excited, it would have to be the "Piwik version" of itself, if you catch my drift.
Makes me think of the concept that telling someone your idea while leave you less likely to act on it, as you'll feel like you've taken a significant step already.