Which modules enable you/account to choose the content (users) to follow?

If you just want to see post by user, there is the Tracker module (included in core). After you enable it you will have tracker/[user-id] and a "Track" tab in user/[user-id]. And of course there is the http://drupal.org/project/views module, with which you can list anything you want in any way you want.

If you are looking for social networking-specific stuff (friends etc), take a look at:
http://drupal.org/project/user_relationships or http://drupal.org/project/friendlist
http://drupal.org/project/microblog
http://drupal.org/project/heartbeat

There is also the http://drupal.org/project/oauth module for external API authentication. See for example http://robloach.net/node/124

Thanks for the info below however, just to be sure or to look a bit more deeply, I would like to ask this:

Can each user create their own content in their account that is based on the people they follow?

Alternately, is there is a facebook Wall type module (that perhaps allows photos ect and could include posts 300 characters or even more )?

Please don't post duplicate threads. I've deleted the dupe. Thanks.