It would be awesome if there was an ability to select/click/highlight points or areas on the graph and then have a floating popup reveal information about what was occurring at that point in time.
For example, if I look at the graph and see a "V" shape cut into the Responsiveness plot line, it would be highly useful if I could mouse over to that "V" on the graph, click, and then a floating popup appears showing what the top-5 CPU-using processes were at that time (or RAM/commit, I/O, Network usage, etc).
Also useful might be graphing timestamps on the X-axis to help correlate what was occurring at those moments. This usefulness would be compounded if there was an ability to choose the time-increments, like 30-sec intervals, 5-min, 15-min, 30/60/etc. Obviously the graphing would change along with these changed intervals.