I played the concert last night at Wolf Trap that featured concert notes available on an iPod. Conductor Emil de Cou developed the idea, and recorded the notes, which were timed to be heard as the music played. I didn't hear the podcast, but Emil told me it was meant to be heard during quiet spots in the music to alert listeners to special features coming ahead in the music.
Before the concert started, Emil spoke to the audience about the concept and asked for a show of hands as to who was using the podcast that evening. I could not tell whether there were more than a few people who responded.
The program was not "difficult" from a listener's perspective, since the music was played while photos provided by NASA were shown on giant screens. To accompany an excerpt of Rite of Spring, the photos were of volcanoes. While we played portions of La Mer the photos were of oceans and underwater life.