Google announced you can now add annotations (i.e. notes) to your AdSense performance charts.
What this means is that you can document a site change or ad type change directly on the charts provided within Google AdSense. For example, if you changed your site layout on a specific day, you can go into Google Adsense and document that right in the AdSense performance chart. Then you can see icons on the report and click on those icons to see your notes. So if you see a spike in earnings, you click on the annotation at that spike and you can associate it with the note you made.
Here are screen shots:
(1) Add annotations by placing your mouse cursor over the chart and clicking +.
(2) This notes box pops up:
(3) The notes are overlaid on the chart and then you can click on them to expand the details of those notes right under the chart:
Forum discussion at WebmasterWorld.