I'd just like to ask if comments made by other members joining some of "my" groups could show in my page or not. At the moment my page just shows my personal comment about my groups activity.
Ning only lists your own activity in your profile page. You can, however, subscribe to email updates about activity on your groups from the group pages themselves. Don't forget to also check your notification settings (http://openanthcoop.ning.com/profiles/profile/emailSettings) to make sure you've asked to be notified of updates to new activity in response to your own posts and comments.
You can also add an RSS feed to your profile for the group content you'd like to see on your page.
For specific discussions, click on the symbol at the bottom of any discussion page that you'd like to receive RSS updates about. Then add that link to your profile as an RSS feed. (To add an RSS feed to your profile page, first grab the URL of the RSS feed you want to display. Next, head to your My Page on the social network and locate the RSS box, which appears at the bottom of the left column by default. Click the "Edit" button.)
Incidentally, the admin team is working on making group activity more visible as a whole, so perhaps there will be another (better and easier!) solution soon.