How to get previous behaviour of alt-tab task switcher in 11.10
Solution 1:
Pressing Tab or the up arrow key ↑ will close the preview.
Solution 2:
I like the previews as well. First, I made sure CompizConfig was installed. I brought it up and disabled static application switcher, then enabled application switcher (there were some keybinding conflicts with Unity's switching behavior, but I just chose to favor the application switcher keys). This worked for me.