Stocks Open Lower; Data, Goldman Weigh  NEW YORK (Reuters) - U.S. stocks opened lower on Thursday,  as investment bank Goldman Sachs Group Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=GS.N target=/stocks/quickinfo/fullquote"&gt;GS.N&lt;/A&gt; reported  smaller-than-expected revenues, while a slew of data gave a  mixed picture of the economy.