Earlier this week Google announced enhanced functionality of the “Top Queries” report within Webmaster Tools. This new function allows you to see more data for your organic phrases. It helps you understand the importance of rankings and the share of clicks you can achieve and you move up the ranking ladder. In teh example images below you can see where you were ranking on specific days and which page was ranking.
I suggest if you have not seen this new functionality you log in and check it out and make it a key part of your ongoing diagnostics.