The latest Nielsen First Alert DVD top 20 sales are up, for week ending 11/6. Note in the chart that 3D sales are being isolated out for the first time. Cars 2 had a 17% 3D share, which is for OD. Since Blu-ray had a 47% share for the title, then the 3D share of the Blu-ray SKUs is 17/47 = 36.1%. That's pretty high considering the low adoption rate of 3D so far. The high percentage can only be explained in that there were a lot of future-proof sales, which is understandable considering that at about only $5 more, the 3D SKU represents the best value (and especially so with Disney titles that also include the digital copy and more special features as an exclusive to the 3D sku).
In the BLu-ray chart, note that Captain America was only 18.8% of what Cars 2 did. It looks like either Cars 2 either did much better than CA, or that CA tanked in week 2(or a combination of both).