i'll probably upgrade in a year or so when the price of the 5d3 has dropped.
the main problem most people had with the 5d2 - the af - has been addressed and whilst i've worked around the small number and awkwardly positioned focus points of the 5d2 pretty well it can be frustrating and limiting at times. more focus points is most welcome.
i can't see there being much of an improvement in IQ at the lower ISOs, certainly not £3000 quid worth of improvement - it would simply be an upgrade to get the better af. the faster fps would be nice, but for me, the biggest limitation is not the fps limit on the mk2, but the fact that in raw the buffer fills up too quickly. for my purposes, the fps rate on the 5d2 was fine anyway.
looks like an excellent camera though, i look forward to seeing some real world shots with it.