Scrolling Text

Here is a script that scrolls a GUI label. It does as @Loius suggested by altering the display string (i.e. it scrolls by characters not pixels). Attach it to an empty game object and set the string, time, and rect. Note that the rectangle needs to be larger than is needed for the string to display on the screen if you want to avoid word clipping. I think you can also turn off the clipping by using a GUI style and setting the clipping property.

 #pragma strict
 var charactersPerSecond : float = 8.0;
 var text : String = "Here is some text to scroll";
 var rect : Rect;
 
 private var textUsing : String;
 private var scrollBasis : String;
 private var scrollText : String;
 
 private var currChar : int = 0;
 private var timer : float = 0.0;
 
 function Start () {
     NewText();
 }
 
 function Update () {
     if (textUsing != text)
         NewText();
 
     var secondsPerCharacter : float = 1.0 / charactersPerSecond;
     if (timer > secondsPerCharacter) {
       var iT : int = Mathf.FloorToInt(timer / secondsPerCharacter);
       currChar = (currChar + iT) % textUsing.Length;
       timer -= iT * secondsPerCharacter;
       scrollText = scrollBasis.Substring(currChar, textUsing.Length);    
     }
     timer += Time.deltaTime;
 }
 
 function OnGUI() {
 GUI.Label(rect, scrollText);
 }
 
 function NewText() {
     textUsing = text;
     scrollBasis = textUsing+textUsing;
     currChar = 0;
     scrollText = scrollBasis.Substring(currChar, textUsing.Length);
     timer = 0.0;
 }