If you also want to follow others' comments on your posts and the posts you've read, every fraction saved off a second is worth the while. In Gmail, saving time with Google+ is without effort, though, and handsomely convenient.
Not only will you get the Google+ notifications you've enabled (for new posts mentioning you, comments on your posts, photos in which you've been tagged, etc.), you can interact with them: adding a further comment is as easy as replying to an email, and you can +1 a comment or posts you particularly like, of course, or flag inappropriate comments.
Comment on Google+ Posts in Gmail
To add a comment to a Google+ post shared with you right from inside Gmail:
- Make sure you receive an email notification at your Gmail address when somebody posts to you directly, mentions you in a post, tags you in a photo or comments on one of your Google+ postings.
- Open the email notification in Gmail.
- The poster or commenter will have "(Google+)" appended to their name, and a Google+ icon will appear next to the message subject and preview.
- Type your comment under Add a comment….
- To find out who can see your comment:
- Click Limited beneath the commenting area.
- If the original post was public and your comment will be visible to all as well, Visible to anyone (public on the web). will appear instead of Limited.
- Click Post comment.
If you try to comment on a post that has been deleted in the meantime, your comment will not be accepted or posted.
See Google+ Comment Updates in Gmail
To make new comments appear in a Google+ post you are viewing in Gmail:
- Make sure you are receiving Google+ notification emails at your Gmail address.
- Open a notification.
- Click Show under New Message from ___ at your Gmail's lower right corner.
- This also works, of course, if you have opened the notification in a new window or tab for watching it.
+1 a Google+ Comment in Gmail or Mark it as Inappropriate
To +1 a Google+ post or comment you like right in Gmail:
- Click +1 (+1 this post) beneath the post or
- +1 (+1 this comment) next to the comment you appreciate.
To flag a Google+ comment as inappropriate in Gmail:
- Click the Flag as inappropriate flag next to the offensive comment.
- Click the red Flagged as inappropriate. flag next to the comment to undo.
(Updated May 2012)