Oh...and...
The way we deal with those who make good returns outside the system is that we tax their Social Security payments. Those with smaller returns pay no tax.
Thank you very much for clearing this, I have been asking this question now for some time but nobody has seen fit to answer me. I seem to have made some mistake, I thought I was diverting my question to the first commentor, probably it was better this way ;). I am surprised to hear that it is not optional, I was sure that this was one of the major differences between US and Europe, that the US government could not dictate you to participate in anything like that or hold a complete registration of its people (wich is neccasery for this to work I presume).
But what surprises me most is learning that the US is much closer to our welfare state than I ever thought, this I will have to use to my advantage in future debates about the "evil America" wich according to the leftists is the most libertarian (classical liberalism) society and see they say, the rich are getting richer and the poor poorer and so many are not health covered and so on and on.
But the trouble is of course that the US is burdened with wealth equalization (distribution) programs just like the rest of us, that are contrary to popular beliew mostly responsible for increasing the divide between rich and poor. The US is much more beurocratistic and even socialistic than I ever thought, but it has also a fearsome champions of freedom, hopefully they will prevail, sadly every time someone gets to Washington they also start to spend...
We have to pay tax on the returns from our pension systems, but similarly to you, there is some kind of taxfree limit (they are very high in Iceland) I beliewe, but we have only recently started private accounts, and I am not sure if they are tax free or not, or if so if it is limitless how much I can put into it.
But at least if I start paying around 3% of my income into it my employeer needs to match it with similar amount. Most likely when people will start to withrdraw money from these accounts they will get less money from the collective accounts, specially as they also bear the burden of disability pension.