I haven't thought it through, but it seems the service would be valuable to consumers if linked to Yelp or other consumer services and it could provide insight into customer service for many companies. It might also be more of a mobile app, but I think there wouldn't be strong adoption if people had to download an app.
Is there anything out there already? I haven't looked.
One positive angle would be to allow people to log something productive or positive they were able to do while waiting.
#waiting dentist 10min brainstormed new twitter service
UPDATE: Bob Coffield twitter stream reveals something along these lines in healthcare...
@iHealthBeat new web-based tool called @MedWaitTime
to check wait times at hospitals and doctor's office: http://bit.ly/9r56Lo#health20