It’s a good thing I never got too far on my annotations software… Google has (will?) release an update to Google Analytics that allows you to mark the timeline with notes. This will help tremendously when trying to identify odd spikes and lulls in the data. Plus, these annotations can live with your account or publicly for all who have access to that account.
Hopefully the API will be updated to allow programatic access to add these annotations. The ability to note specific events in an automated manner would make the feature much more useful.
Video below, or learn more at the GA Blog.