I think one problem with Metro adoption has actually been the way one browser vendor in particular treated its users. I'm talking, of course, of Google Chrome. For a long period of time, reinstalling Chrome meant getting dropped into a hideous, single-window "Metro" implementation that offered none of the benefits of the environment, and every downside. I would prefer to use IE in full screen mode over "Chrome in Windows 8 Mode" and that's saying something.
Now Google's "Windows 8 Mode" is essentially a ChromeOS implementation in Windows, which I sort of think is cool, and mostly think is just perplexing for users.
I wonder why no one - Mozilla, Google, Opera - has implemented exactly what IE does. A very simple interface with not a lot of bells and whistles, an address bar, a tab picker, and a full screen browser. Maybe it's because Google Chrome doesn't seem to work well with multitouch - support seems to be based on the whims of the version number - and Mozilla's engine similarly seems to have interactivity issues.
As a result, I get the feeling when using these browsers on a Surface Pro that no one at Google or Mozilla is too. For over a year, pinch to zoom and other multi-touch gestures didn't work on Chrome. Or they would on Canary or Dev, but only for a few weeks, before suddenly not working again. Pinch to zoom is abhorrent on Firefox - a clunky experience that makes me regret doing it every time. And scrolling requires two fingers on Firefox - or at least it does in Nightly now - and so for the longest time I thought it didn't work at all. I don't know why they've decided their browser is the only one that needs two fingers to scroll. Chrome works terribly on a mid to high DPI display. I can't for the life of me close a tab.
The result is clunky. Users don't want clunky things. Chrome defaulting to Metro mode for Windows 8 users during a period when the browser barely or intermittently supported touch leaves me with only foul things to say to a Chrome dev or their program manager if I ever meet one. Likewise, I can't understand why Firefox is making Firefox in Metro a major project - give me a full screen interface to Gecko with a big address bar at the top or bottom and let me use that.
EDIT: WHOA! Firefox Nightly's (30.x) Windows 8 mode is actually decent. Pinching to zoom doesn't inflict masochistic terrors on me, and one finger is all that's necessary to scroll. When did this happen and why doesn't someone tell people about it?