Q:

Getter vs Computed property. What would warrant using one of these approaches over the other?

Take a look at this variable
var username: String {
    get {
        return self.twitterAccount.valueForKey("username") as! String
    }
}

The compiler doesn't complain when I remove the get, presumably because it is simply treated as a computed property.
var username: String {
    return self.twitterAccount.valueForKey("username") as! String
}

What would warrant using one of these approaches over the other ?

A:

Both forms are exactly the same thing, a read-only computed property.
From the documentation:

You can simplify the declaration of a read-only computed property by
  removing the get keyword and its braces.

