You could also use the pen tool to create a vector mask and clear the background. That'll give you clean edges. If you want some of the parts smoother, you can always apply the vector mask and create a new layer mask to work with.
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Mephistoles
Heh, I've been using the pen tool to render images for quite some time, in my opinion it's better than using an eraser (though it might take longer than the eraser, it could be used to render images better)