Of course the metro UI has advantages on a tablet, my post was mainly centered around the workstation. Whether you take your workstation with you at the end of the day or not is irrelevant for the work you do on it when it is being used as workstation.
If you feel the transition between the two isn't smooth enough that's another point but my first reaction to this is positive. I do not want that transition to be smooth, to me that's like trying to mimic the feel of a nice heated leather car seat while skydiving. If either was any like the other at least one of them would be worthless (probably both).
Realizing that that is impossible and separating them is the key to my heart and both windows 8 and unbuntu for android seems promising in that regard (but since I haven't used any of them that is just my initial impression). Apple on the other hand seems to be taking small steps in the opposite direction with mountain lion, which is of course fine for most but I don't think that that will cut it in the long run.