this is just a code-style comment, but I prefer to return from a function block rather than putting stuff into an if statement. e.g.

```
function() {
  if(conditionNotOk) return;
  // bla
}
```

instead of 

```
function() {
if(conditionOK) {
  // bla
}
```

... of course I also have heard people refer to that practice as a 'modern-day GOTO'. Me, I just don't like to indent too much, if possible.

Also, you're using the backbone models `fetch` method to post data. The intended way to do that is to create the model with the data and then call `save` on it. something like this:

```
var instance = new app.models.Model({
  post_id: id,
  text: text
});
instance.save();
```

see http://backbonejs.org/#Model-save for more info. And always make sure you check whether the request to the server was successful (maybe reflect that in the UI somehow) or show a (flash-)message if it wasn't.