I kind of agree with a lot of the opinions being offered here... but it's a real shame. I don't like the tile UI that much, and I certainly don't like the weirdness of the "start menu"- but I'm glad to see Microsoft innovating/trying something different- just like with Windows Phone (which also looks to be a flop) they're actually standing out from the rest of the crowd and doing something unusual with their OS.
I initially struggled with the Ribbon (and there's a great post here http://blogs.msdn.co...y-of-the-ribbon.aspx
about it) - but there's two reasons why I came to settle down with it- use and acceptance that I'm not all IT users. You've got to use it day-in, day-out in order to BREAK the habit of the old system- and that's the main reason people become efficient with desktop/office OS (come on, how many of us really associate scissors with moving text on a written page- an appalling visual metaphor!). And I also realised I'm a power user, and I'm happy with shortcut keys and such like therefore changes in UI probably aren't aimed at me- they're aimed at people who haven't used computers for years, or are young and developing their skills.
Now Windows 8 offers a similarly scary set of changes - some of which are double-edged swords (new ui: new learning curve, but a change to make tablet PC's work like desktops; new marketplace: a secure way to get apps to people (and to get people to pay for them- great for donation coders, surely!), but with Microsoft vetting)- but I'm excited about change!