Maybe iOS is just a bridge to the future interface, but Metro UI is a failure on desktop. Only about 50% of those who tried the Windows 8 Developer Preview liked the UI on desktop.
About 100% of people who draw conclusions from negative comments on developer preview software should be ignored. Joke aside, it could've been 100% (and meant just as little). Come launch, we'll know. Before then, expecting a flaw-less solution is just an indication of a flawed mind.
addendum:
guess i might expand some on this, or rather, two of the main concerns raised: navigating metro without touch, and new start conflicting with expected behavior of start menu of old.
First, i suspect that touch-mouses (think: magic mouse) will be pushed hard come launch. Until 2014, W8 will mainly be sold with new devices (it will take enterprises roughly 18 months to migrate). New devices are likely to have these mouses. This takes care of the scrolling issue that some users have reported. For obvious reasons, track-pads on laptops will perform the same function (i would assume that they already do, by default). If true, this problem will not be much of a problem at all.
Second, while the conflict in behavior is a quite serious issue - as shown by the wide-spread criticism, this is a somewhat easy fix. For example, one could make the start menu open on hover, or (perhaps better*) hold. After all, one can expect that the average user really cares **** about the start menu, and that it, in fact, is a bitch to navigate for most (most, i would assume, use it to locate some program in a nested file structure). Those who do care, and want to use it in desktop-mode, are savvy enough to learn the new behavior in a flash. Further, I would assume that the most used feature in the start-menu nowadays is Windows equivalent of "spotlight". From what i have gathered this is integrated well into the start experience.
So yeah. There are issues to be solved, but these issues have fairly straight forward, accessible, solutions. Thus, once more, wait for launch. Then, and only then, can we accurately judge whether or not Metro will work on desktops or not. I, for one, see no real issue here. I may not be a user who necessarily would prefer it, but overall i think its a good idea.
Oh, and a third point, aka "the enterprise issue". If testing shows that enterprises really wants this feature out, they will surely have the option to disable it. Think people are exaggerating though. Its not like people spend hours in their start menu, and theres no reason to believe that Metro will make them spend more time either. If its about enterprises not wanting users to have "games n ****" in their work environment, well... MSFT have nice solutions for that as is.
* better because it would not interfere with average joe who i suspect would like to get rid of it anyway.
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thank you, sir.