Programmers and the air staff have been adding new 'tricks' or 'techniques' for years to try and improve the performance in delivering audience (ratings). Recycling the audience to other dayparts with cross promos, billboards to tempt listening through the stop set, big events to build huge tune in, daily features to build certain hours in the day (the Request Lunch), listening locations (at work) and also special programming days (All Music Mondays - 2 Fer Tues).
Over the last 5 years the new big tool has been Appointment Listening. Making a specific appointment with the listener to come back. While it may be similar to the 'billboard just before the stop set' it really serves a different purpose. Really this technique stems from the 'Arbitron Listening Fact' that you have an 'average time spent listening' for the station for every time they tune in. Say the average TSL with the station per tune in is 8 minutes - so they are in the process or already have spent 8 minutes - if you can get them back in 15 minutes you will probably get another 8 minutes. So your total here is 15-16 minutes. At the end of the 2nd tune in maybe you can hook them for another 8 minutes and end up with 20+ minutes in a 90 minute period.
Instead of begging them to stick around through the stop set and hope they will hang for another 8 minutes now we give in to the 'law of averages' and shoot for them to come back later in the hour or maybe later in the daypart (at 12:30 catch the big Concern Announcement for U2).
It's an effective tool and it has been shown in lots of data analysis to work. Of course the best way to see it is in tracking the PPM meters where we can see real behavior in real time. Who knows if any of these techniques is really accurately recorded in a diary? Hence we now see the Appointment Billboard being the new big standout technique in the jock breaks in PPM markets and also making it's way to diary markets. It's even bleeding into TV - just watch SportsCenter.
The key here is to make sure you have real actionable appointments. Just mentioning that 3 Doors Down's recurrent from last year is coming up in 15 minutes will probably not do much. Make sure to make it big and newsworthy or entertaining enough to catch the attention of the audience.