If you have common activities in your sales process that you want to keep track of and measure over time, you should give Note and Task Types a look.
For example, when taking a note, you can choose what type of note it is:
Once you save the note, you can see that the note type is displayed in the activity history:
After you've taken several notes with the note type set, you can head over to the Notes Over Time by Type report:
And you can see them added up by time period:
If you want to see the individual notes, just click on a particular segment and you can drill down to see the individual notes:
If you are an Admin, you can change the list of Note or Task Types by hovering over the gear icon next to the Type dropdown:
Then enter any new options in the list and click Modify: