Gadgets, which used to be confined to the Sidebar in Vista, are now permitted to roam all over the desktop. I still don't understand why anyone would want them, but apparently enough people would find it useful so Microsoft has a Gadgets option right on the desktop's context menu.

The Explorer hasn't changed, and of course it still uses those absolutely stupid "contextual strips" which changes depending on what is selected (a huge no-no).

Search has been drastically changed. The search window has been removed, and instead you are supposed to use the new search bar in the corner of every window, just like a web browser.
Since the search window has been removed, most of the advanced options have been removed as well.

I don't know about you, but I avoid using search bars in browsers because they can point to unknown search engines. If I want to search I usually just open a new tab and go straight to www.google.ca in the URL bar.

The old Security Center has been changed into this new Action Center, which now displays more than just security-related things.

I actually find it quite annoying most of the time, because it constantly puts up messages about Windows Backup, and it also wants me to set up Automatic Updates, even though I run updates manually since I got sick and tired of Windows rebooting my computer all the time, and I also use my own backup program.
Any message that shows up can be turned off, but doing so turns off everything for that particular piece of the Action Center, which is slightly counter-intuitive.

Tiling is not new in Windows, however, in addition to the options in the Taskbar context menu, dragging the window to the side of the screen tiles it to that particular side, and dragging to the top maximizes the window. As you are dragging the window, it displays a little transparent box around the new window location.