Made slight progress. Reflected the code and found the DataTableConverter in the Preview assembly that comes with the CTP Beta. Added the following to my web.config:

Argh. This just sucks. 

OK. I think after digging around I've got it. At least it appears as such.

 First thing, after adding a reference to the Preview CTP Beta assembly, and adding the converter for the data table to your web.config, then make sure you add the PreviewScript.js to your project, and add a reference to it in your pages ScriptReference tag, in the ScriptManager. Then, once you have that, then you can instantiate a new DataTable, like so:

 <snip>

onGetAllTabsComplete: function(tbl) {
                if (tbl != null) {
                    eval('var tblrows = ' + tbl.dataArray.slice(0, tbl.dataArray.length-1) + ';');            <-- NOTE THIS LINE. I THINK THERE'S A BUG, SINCE THE dataArray has a trailing ')'.        
                    tbl = new Sys.Preview.Data.DataTable(tbl.columns, tblrows);
                    for (var i = 0; i < tbl.get_length(); i++) {
                        var row = tbl.getItem(i);               
                        _editor.createTabNode(row.getProperty("ID"), row.getProperty("Title"), row.getProperty("MenuItemID"));
                    }
                }   

</snip>

Atlas team, what in the hell is up?! This is, frankly, one of the most bass-ackwards releases I've ever seen from you guys. How, after so many friggin CTP's, do you just bust out and drop this crap on us.

Pissed in San Antonio,

William

 I use Preview CTP Norvember Beta assembly, and make client source as follow.

 tbl = new Sys.Preview.Data.DataTable(tbl.columns, tblrows);

No matter how tbl.columns and tblrows is not null, I get the result zero of  tbl.get_length();

Why?

Maybe bug of Sys.Preview.Data.DataTable creator.

In Microsoft.Web.Resources.ScriptLibrary.PreviewScript.js, when the Sys.Preview.Data.DataTable instance create,

to compare Array type and arguments tbl.columns and  tblrows is mistake.

Hence, I'll modify the client source as follow.

function Button1_onclick() {
    var results = GauceWebService.Select(OnSuccess);
    return false;
}

function OnSuccess(result)
{
     var tblrows = new Array();
     var tblcols = new Array();
     var strRowsData = "";
     var strColssData = "";
       
     if (result != null)
     {
     //debugger;
        result.dataArray = result.dataArray.slice(0, result.dataArray.length-1);   
   
        strRowsData = result.dataArray.substring(1);
        strRowsData = strRowsData.substring(0, strRowsData.length-1);
       
        tblrows = strRowsData.split("},{");
        for(var j=0; j< tblrows.length; j++)
        {
            if(j==0)
            {
                tblrows[j] = tblrows[j].toString().substring(1);
            }
            else if(j==tblrows.length-1)
            {
                tblrows[j] = tblrows[j].toString().substring(0, tblrows[j].toString().length-1);
            }           
        }
       
        strColssData = result.columns.substring(1);
        strColssData = strColssData.substring(0, strColssData.length-1);
        //alert("strColssData = " + strColssData);
        tblcols = strColssData.split("),");
      
        for(var j=0; j< tblcols.length; j++)
        {
            if(j< tblcols.length-1)
            {
                tblcols[j] = tblcols[j].toString() + ")";
            }
        }
    
        //result = new Sys.Preview.Data.DataTable(result.columns, tblrows);  // Maybe result.columns and tblrows type are string...
        result = new Sys.Preview.Data.DataTable(tblcols, tblrows);
        //alert("result.get_length() = " + result.get_length());
        for (var i = 0; i < result.get_length(); i++) {
            var row = result.getItem(i);  
            alert("Row[" + (i+1) + "] \r\n" + "Name=" + getProperty(row, "Name") + "\r\n" + "LastName=" + getProperty(row, "LastName") + "\r\n" + "Email=" + getProperty(row, "Email"));
            //alert("Name=" + row.getProperty("Name") + "," + "LastName=" + row.getProperty("LastName") + "," + "Email=" + row.getProperty("Email"));
       }
    }

}

function getProperty(rowObj, name)
{
    var rowstring = rowObj._row;
    var strColValue = "";
    var strKeyName = "\"" + name + "\":";
    var nLastIndex = rowstring.lastIndexOf(strKeyName);
   
    if(nLastIndex == -1)
    {
        return "";
    }
    else
    {
        var strTmpValue = rowstring.substring(nLastIndex + strKeyName.length-1);
      
        if(strTmpValue.indexOf(",") == -1)
            strColValue = strTmpValue.substring(2, strTmpValue.length-1);
        else
            strColValue = strTmpValue.substring(2, strTmpValue.indexOf(",")-1);
    }
   
    return strColValue;
}