IMHO Microsoft has gone from the best UI to a horrible UI. No way of visually discerning what is a button or other GUI component and what isn't is not a improvement! The revolt due to their absurd VS GUI a while back is a great example, but it's the subtle UI changes in their current offerings that are most frustrating.
I switched to linux a while ago, and it has a long way to go ... but its an upward curve vs. Apple/MS's downward spiral when it comes to UI.