Observing the Hearbeat of an Event

How might one observe the Twitter ‘heartbeat’ of participants at an event?  How about creating a Twitter list of the participants and using the Twitte StreamGraphs service I mentioned previously as it can display a timeline of tweets for a Twitter list as well as a hashtag,

Examples are available for the UKOLN’s Evidence, Impact, Metrics workshop and the IWMW 2011 event.