I put the word "foo" in the text input box between "Search:" and the
pulldown that says "Current Folder".  For people that seldom use this
feature, it might not be obvious that one needs to press "Enter" to
actually perform the search.

It is also probably not intuitive that one can click on the binoculars
icon to change how the search is performed.  After I change the
selection from "Subject or Sender contains" to "Recipients contain", I
would assume that the search has been performed.  It took me several
frustrated searches to figure out that I also need to press "Enter" in
the text box in order to actually perform the search.

evolution-2.12.3-1.fc8