I came across an interesting post over at interuserface which looks at the different shapes that have been owned and are synonymous with their respective platforms. What was also intriguing was how it laid out the shapes.
It seems that the shapes gradually morph into a square. Interuserface explains:
Microsoft’s Metro UI owns the square. Apple has a corner on the roundrect, from the Springboard launcher to the iPhone hardware itself. Nokia, despite its late entry with MeeGo’s Harmattan UI, found the squircle unclaimed and ran with it beautifully. Palm has used the circle from the early days of PalmOS, and in WebOS, HP continues the tradition with care (one might even note that both Palm and HP structure their wordmarks around the circle).
Read the post by interuserface.