I think a Smart Diary like journal is a good idea for Google+, where one can make a diary like entry for a day, making it an online and cloud-connected, virtual diary powered by the backbone of Google and its services.
With the power of Google Docs, the visual cues of the card-like look and the power of Google, it can be an unparalleled experience.
For example, we can have two columns of the page, with one long pane on one side for the user to write the content.
And, the other side having multiple cards, one below the other, each having recommendations from the various sections of Google such as ...Details of location from Google+ Locations or My Tracks suggesting lines like "Been to Hiking"
..."Celebrated Father's Birthday" based on Google+ Events and/or birthday details of Contacts.
...The best of the geo-tagged photos (as seen by Google+ Photos) can be shown as suggestions to add photo the the document to add to an "auto-awesome"experience.
...Suggestions from Google Search history can be shown as "Read the article on www.example.com
...Any other suggestion from the content in Google Now (if the account is connected to a mobile device).
In the end, such pages can be exported to a Yearbook like document which will hold all the entries of a year.