I tend to look at it in the light that User Freedom is (in most cases) directly proportional to Developer Freedom.

It's true that 2 different browser engines are going to use more resident memory, and CPU cycles if both are in active use simultaneously. The same is true of including both GTK+ and QT4 widget libraries.

I really only think we will see a significant battery hit if developers misuse the feature, and ignore these relevant concerns, the same problems we already see with native widgets and apps.

It fits with nokia's stated vision of Maemo, the desktop experience on a mobile. How many rendering engines do you have installed on your desktop?

We're still on the cusp of such an experience being at all feasible on devices of this size. But the amount of memory nokia will be able to cram into these is only going to get bigger.