The performance vs. time graph is great! Here's an idea for a similar graph which might be interesting as well.
The graph is a user-customizable bar graph of wins, losses, and draws vs. time. The x-axis is spit into chunks of time, say months, for example. In each month, there is one bar representing the number of wins, a second bar for the number of draws, and a third bar for the number of losses.
To really make it cool, you allow the user to filter which games are being shown.
One set of options (maybe with radio buttons) could be:
x As Black
x As White
You could also filter by opponent rating:
Min. Opponent Rating: x
Max. Opponent Rating: x
Then set the starting and ending dates:
Starting Date: x
Ending Date: x
And set the size of the time intervals used on the x-axis:
X 3 Months
x 6 Months
After all, I would like to know if my game is improving as black vs. opponents rated over 1200!!!