I no longer have to do Ctrl+Esc, R before I can type something to run (I'm a huge keyboard guy); I just have to type Ctrl+Esc and start typing. This savings alone has ruined me for XP. (And before you point out that I can just use Win+R, I don't like the Windows key: it's not on all keyboards and it's not always in the same place.)
If I want to search for a program in my voluminous start menu, I just do Ctrl+Esc and start typing. When the list of results contains my target, I press the down arrow to pick the one I want and press Enter when I get there.
If I want to search for content on my computer, I just do Ctrl+Esc and start typing (once search is set to index my entire computer -- I wish that were the default). If I want to be specific that I just want to search content or file name, I can use the "content:" and "name:" designators, e.g. "content:foo name:foo.cs".
If I want to find a setting in a particular control panel app, I open the control panel and start typing -- the results point me at the specific control panel applet and page with that setting.
If I want to find something on the internet, I press Ctrl+Esc and start typing, then press the up arrow (to get to the "Search the Internet" option) and press Enter, which brings up the results in my IE7 favorite search engine.
If I want to find something in my large list of installed programs, I open the Programs and Features control panel and start typing (I found the renamed "Add and Remove Programs" control panel by searching for "uninstall").
Before you narrow my list of likes about Vista to "pervasive search" (which, obviously, I love), I also really like the sidebar. It's amazing how often I glance over there to get some quick piece of info that's always being updated for me rather than start some app, interrupting what I'm doing (e.g. lately I've been waiting with bated breath for MSFT to hit 30). I'm anxious for lots more sidebar gadgets.
I love that the desktop is in the Alt+Tab list.
I love the 3D Win+Tab list.
The games, both new and old, are uniformly gorgeous.
I really love the new look 'n' feel, including the animations and the new start menu, both of which I turned off in XP.
I love that it just works on my 2-year old Dell laptop w/o any muss or fuss. I only have a Windows Experience Index of 2.0 because of my graphics card, but using Vista is still a very pleasant experience (and I have Aero glass around the edges of my windows and everything).
I really love Windows Meeting Space. I'm a big user of Live Meeting because of my remote employee status and Windows MS is a simpler, cleaner, peer-to-peer version of the only parts of LiveMeeting I every actually used, i.e. sharing apps and sharing files. To have it included for free is huge.
I love having Media Center included, too.
I love that I can do picture slide shows from zip files as well as from folders.
I like the new Sync Center, one-stop shopping for my offline folders (which I love) as well as managing my smartphone's files.
I really like the real-time thumbnail of apps when I hang the mouse over icons in the taskbar and in the Alt+Tab/Win+Tab list.
I love that .NET 3.0 is included out of the box.
I love that every app I've tried, including an app I originally wrote for Windows 95, just works.
I love that I find new features all the time.
As I've mentioned, I like the clearification.com site. In fact, I liked it so much, Mel and I want to see Demetri Martin live in Portland. Very funny.