I think it's important for parents to make sure that their kids have some time to do nothing, get bored, and find their own mischief and passions. It's a tough balancing act.
Sometimes I'd go check out what my father was doing in his workshop, and he'd show me how to use the tools or teach me the theories behind whatever he was working on (construction, metal work, electronics, magnetism, etc). It was up to me to decide if I was interested enough to try my own hand at it, and there was no fallout if I decided after starting that I wasn't interested after all.
As a result, we've grown up to be independent thinkers. We don't depend on other people to give our lives meaning or to give us structure. And most importantly, we're all very creative.
Kids will find things to be interested in so long as you don't smother them or stunt their independence.
The twin studies I'm aware of basically say that you can expose twins to identical circumstances and they will still turn out different. I'm not sure how that contradicts his main point though.
Incidentally, my upbringing sounds a lot like kstenerud's. My brother and myself sound much like he and his siblings. Another anecdote, sure, but still an intriguing point of view.
Spot-on, at least in my experience. My parents pounded into me a piece of wisdom- "Boredom is a choice". It seems to have paid off.
It's really great to have them involved in things even if it's a lot of things. They'll tell you if they really don't like it. Don't confuse laziness or tiredness with disinterest, that's all. You never know if you did right until much later. All you can do is try what you think is best, hold your breath, and let the chips fall where they may.
A lot of times I think it all depends on the kid too. I was signed up for everything from swimming lessons to soccer to boy scouts and more before I even turned 1! That's right, before I was a year old! All things considered I turned out smart and productive.
My younger sister on the other hand wasn't very involved. My mom dragged her to girl scouts for a good 4 years or so and she hated it though it probably did her good. But she's great too! She's a straight A student coming up on graduating from Penn State in about a year.
So it's all just relative.