Market preview: U.S. stock futures riding high, possibly due to a number of factors, not least...

|By:, SA News Editor
Market preview: U.S. stock futures riding high, possibly due to a number of factors, not least strong weekly jobless data - till next week's revision at least. S&P benchmark +0.5%. An upgrade of U.S. stocks by Citigroup may also be boosting sentiment as markets on both sides of the Atlantic brush off S&P's downgrade of Spain. Sprint jumps 17.3% on buyout speculation involving Japan's Softbank, with Clearwire soaring as well. Later: Fed's Plosser