Best way to double size of images for Retina display?

Question

I have a number of regular-sized (@x1) images that I use in my iPhone app. Outside of redesigning them from scratch in hi-resolution, what is the best way to double their size & resolution using Photoshop?

Answer 1

Well, personally I prefer this way:

Resize the psd 200% and double every blending-option (for example if your stroke was 1px thick, change this into 2px, same for drop-shadow and stuff).

However, this is how (I think) Apple does this:

Resize the psd 200% but don't double any blending-option (Apple uses very thin strokes on the iPhone 4).