In case you're wondering, I have a WP7 and I think I'd find it distracting if everything were circles. It's hard to detect size differences with circles...I think I would not be able to focus on anything. Squares are better for repeated differences. Even though it's more boring to glance at boxes, since they're all mostly the same shape, the deviation from sameness stands out more. I guess you don't argue it's efficiency, but I'd take efficiency over coolness in this scenario as I use the phone every day between class.