A really neat toy ( obviously nothing essential) woud be a "selective focus" tool to achieve effects similarly to the lensbaby lenses.
I am thinking of a circular or oval selection ( that can be moved around freely) with steadly increasing blur towards the edges of the image (up to a selectable maximum value). Perhaps it would be good to have a lens-blur algorithm instead of the common gaussian blur.
Examples of the desired effect can be viewed for example here:
A software emulation can not be expected to be perfect but perhaps better than carrying around another lens.