I just posted this wherein Dave Wiskus suggests we are growing out of its utility. I'm not sure if I agree with him. I got my first chance to play with a windows phone the other day, and it feels a little flat. IMO just adding a bit of dropshadow makes it more like something you want to touch. Mine is on the right.
Don't get me wrong. I'm not suggesting that my version is a success. I think the problems run deeper than drop shadows. b_b and I were just laughing about how funny it would be if you designed a keyboard this way. The 'e' might be so big you could slap it with your palm, and 'q' so small that you'd have to grab a stylus to tap it. :)
What confuses me the most is how little sense any of the tile sizes make. On a brand new Lumia 920 (supposedly the flagship WP8 phone) random things are huge, and other things are tiny. Every default Windows app seemed to have a Nokia duplicate thrown in as well.