I think many of the ideas you guys are offering for "girl products" are still a tick too complex and techy. I think, if I would want to get a young girl started with electronics I would start without an arduino, but just getting her familiar with simple circuits. I think the perfect starting product would be lady ada's minty boost.
http://www.ladyada.net/make/mintyboost/
If I where to design new gadgets for girls, I would start from there - analyze why this was succesfull and create something with similar proporties. We see here, the usefullness of this itam is very obvious and direct, while the complexety of the design is low and very basic. Also, the overall design is smart and appealing.
p.