These are for select markets. San Fran up 50%. I guess libs actually do tune in during these things. And these are what's known as PPM markets, or "Personal People Meter" an electronic media monitor that survey participants wear. Smaller markets have a diary reporting system.
It's most likely a curiousity spike and will likely come down, at least some, the way spikes do. Funny how word of this coincided with a new push to get rid of Rush Limbaugh. I don't think it's a coincidence. The reality is this controversy is over and Rush has survived.
I should note however that after a sluggish start, Mike Huckabee's show seems to be improving, somewhat. But at the moment, it doesn't appear to offer a serious threat to the King of Talk Radio.