My experience is more like pg describes, where I had a lot of trouble projecting what it would be like, and in retrospect all the rational pro/con analysis I did wasn't really getting to the core of the matter.
The question I'm attempting to answer with data is: how likely is it that I would experience the "switch flip" that Paul describes here, and would it be enough to overcome the feelings I have about it now? If the data strongly indicated that most parents experience this kind of "switch flip", it would make me more inclined.
I strongly disagree that this gives good evidence whether you'll enjoy having kids yourself. I never liked dealing with kids of any age; the experience with my own kids, however, is vastly different, and I really enjoy their company.
Obviously these activities do not capture huge things about the 24/7 job that being a parent is, but they will probably tell you a lot more about how you relate to children than looking at population self-report data.