Sorting of Spotlight's search results is disabled in Lion I can't sort Spotlight's search results - sorting by Name, Date Modified, et. al appears to be disabled.  Google seems to be useless in finding a resolution to this - although I suspect a previous installation of Quicksilver had something to do with this.

I have forced Spotlight to reindex, but it still doesn't work.

Finder otherwise functions normally.
Finder has two different sorting modes (the new Arrange By and the old Sort By) on Lion. If the Arrange By mode is set to something other than none, you can't sort columns in list view by clicking the list headers.

So just select View > Arrange By > None.