Very good post Eurograff. Let me see if I can add a few items without making myself look silly in comparison
The explanation I have normally seen is that in France, employing people is very risky since you may not be able to fire them, and they are expensive. Hence you hire the best people you can and give them lots of stuff to help them do more work (machines, training, whatever). i.e. you add more capital per unit of labour. Whereas in the US or UK you might just hire a few more cheap unskilled people on the basis that you can fire them easily if things go bad. This gives very productive workers but not many jobs in France, vice-versa in the US.
I believe it is currently negative. The average american is reducing their net asset value, and has been for several years.
Paul in Saudi - I believe the ‘savings rate’ usually referred to in these situations covers everything you refer to in your post, not just the amount you have saved in the bank. How much money you earn minus how much you spend, basically. In the US this is negative because cashing out house equity and spending it is such a popular hobby. Which means when you retire you should have plenty of neighbours willing to work for food. 
French taxes are not excessively high by European standards. Nor is the proportion of people who are ‘unemployable’. Although they don’t help the situation, other countries cope reasonably OK. The real killer is probably excessive labour-market rigidity. As well as all the red tape around hiring and firing, apparently there are lots of rules around who can do what jobs - you need a diploma in hairdressing before you can cut people’s hair, and so on and so forth. Whereas in the UK you just need scissors and self-confidence.
gitfiddle - Despite its reputation, France does not have that many man/days lost to strikes, lower than the UK if I recall correctly, although this may be an artefact due to different national measures or whatever. My impression is that french strikes tend to be more coordinated and visible, but fewer in number.
Lemur866 - The Economist had a very interesting article about this sort of thing a few issues back, basically on the premise that western countries have built up their social rules along two dimensions - job security for the employed, and assistance for the unemployed. Some countries (like France & Germany) are high on both dimensions, some (like the US) are weak on both, others mix and match (I think Sweden was quoted as being medium on job security but high on social assistance). There are pros and cons to every combination. But yes, every developed country without exception has rules about firing people and some sort of welfare for the indigent - it’s pretty much part of the definition of ‘developed’ that the poor aren’t starving on the streets and workers aren’t excessively abused.