Pianistically, Samuel Barber's art songs can run the gamut from simple and sightreadable to eye-crossingly difficult. Most pianists will be familiar with "Sure on this Shining Night," "The Daisies" and "The Monk and his Cat". Other songs, such as "Nocturne", "I Hear an Army" and "O Boundless, Boundless Evening" are definitely in the 'difficult' category, and it is helpful to send the music ahead of time for your pianist (especially if they have not heard of the piece). Along the same lines, these songs probably should not be brought to a recording session for a pianist to sightread.
Just a friendly reminder!