Some thoughts...
On teenagers: when I turned 17 I was most eager to start driving, for independence, for fun and because all my mates were doing it... maybe not a brilliant excuse but it was probably a factor. It was rather expensive but I think it's worth it. Now I'm at uni I have less need for the car because I can walk or bus round Leeds but at home it's such a blessing. However, apparently my old head of sixth form is the only one in our area who hasn't been to the funeral of a sixth-former involved in a driving accident... sobering indeed.
On dual carriageways: my main problem was that I was slightly nervous joining from a slip road so I used to spend too long checking behind me for traffic, resulting in a bit of weaving. Ulp. Then I realised a short glance was enough, and that mirrors are my friend
On the other hand though, when pulling out to overtake, I always forgot to check my blind spot. That nearly caused a collision... never made that mistake again.
On roundabouts: people should know better about lane usage (my dad's terrible) - unless it's labelled otherwise, stick to the left lane for going left or straight ahead, depending on how many exits there are. In the case of one of my local roundabouts, there are only two exits really so there is some confusion about which lane to use to go straight ahead. My friend took the left lane, a wagon took the right. Result: a clipped car and a wagon driver who didn't care or didn't notice.
On Paris: the use of bumpers when parking is ridiculous. Am I right in thinking people deliberately leave their handbrakes slightly loose so that people can nudge them..? And those silly rules Topher posted remind me of the
Indian rules of the road... classic material.