Here is a Twitter StreamGraph created from the query "American Idol" OR #idol in the date range of May 3-21, 2009. I had to use a custom version of my tool that used tweet data harvested in a different manner from the online version which is limited to viewing the last 1000 tweets only. Given such a popular topic, 1000 tweets only goes back a few minutes and is uninteresting.
A couple of observations:
It would be interesting to see the graph for a longer time period but Twitter Search is currently only returning data that goes back around 21 days.