Gmap / Gmaps

Unfortunately, you can't. You could open an issue in the GMap queue to add location fields to the status update form, but I would put the likelihood of the GMap maintainer(s) agreeing to include that at "extremely low." It is a feature I would eventually like to see, but it's not likely to come about until sometime late in the Drupal 7 cycle, if then.

Having said that, it probably wouldn't be a particularly difficult task for anyone who understands hook_form_alter() to write a short integration module, but I'm not going to do it.

Each concept has its advantages. You could, of course, set up a very similar system using nodes if you wish. Someone once built a Twitter clone in Drupal using nodes that looked and worked almost exactly the same as Twitter... I've misplaced the link though.