Meanwhile, over in New Zealand the first results are starting to emerge from the introduction of their KiwiSaver pension system. This isn't miles away from the Perosnal Accounts model being developed in the UK, and is using the auto-enrolment plus opt-out model of membership. You can find some stats on how it is doing here.
It looks like the opt-out rate is about 15%, so that would suggest that membership is going to be pretty large. Notably membership so far doesn't seem to vary much between age groups, or by gender. The second point is a key one. One of the successes of the mandatory superannuation system in Australia was that it massively boosted the number of women with funded pension provision. In addition there doesn't seem to be much of a levelling-down effect so far.
A couple of points, one serious and one silly. First up the Pensions Policy Institute makes the point that the KiwiSaver isn't directly comparable to Personal Accounts, which they expect to have more of a levelling down effect.
Secondly I see that the NZ government website on which you can find reports about the success of KiwiSaver shares the same name as that of Scottish Life's Steve Bee, who seems to be on a personal crusade to undermine confidence in the UK equivalent (for example).